Plasma Carotenoids and Recurrence-Free Survival in Women With a History of Breast Cancer
http://www.100md.com
《临床肿瘤学》
the Departments of Family and Preventive Medicine and Psychiatry, and Cancer Prevention and Control Program, University of California, San Diego, San Diego
Division of Research, Kaiser Permanente Northern California, Oakland, CA
Arizona Cancer Center, University of Arizona, Tucson, AZ
M.D. Anderson Cancer Center, The University of Texas, Houston, TX
the Women's Healthy Eating and Living Study Group
ABSTRACT
PURPOSE: Previous studies suggest that diet may affect recurrence or survival rates in women who have been diagnosed with breast cancer. The purpose of this study was to examine the relationship between plasma carotenoid concentration, as a biomarker of vegetable and fruit intake, and risk for a new breast cancer event in a cohort of women with a history of early-stage breast cancer.
METHODS: Participants were 1,551 women previously treated for breast cancer who were randomly assigned to the control arm of a diet intervention trial between March 1995 and November 2000. Outcome events were probed during semiannual interviews and verified by medical record review. During the period under study, 205 women had a recurrence or new primary breast cancer. Plasma carotenoid concentrations were measured in baseline blood samples. Hazard ratios (HR) and 95% CIs by quartiles of plasma carotenoids were computed, controlling for tumor stage, grade, and hormone receptor status; chemotherapy and tamoxifen therapy; clinical site; age at diagnosis; body mass index; and plasma cholesterol concentration.
RESULTS: Women in the highest quartile of plasma total carotenoid concentration had significantly reduced risk for a new breast cancer event (HR, 0.57; 95% CI, 0.37 to 0.89), controlled for covariates influencing breast cancer prognosis.
CONCLUSION: Plasma carotenoids are a biologic marker of intake of vegetables and fruit, so this observation supports findings from previous studies that have linked increased vegetable and fruit intake with greater likelihood of recurrence-free survival in women who have been diagnosed with early-stage breast cancer.
INTRODUCTION
Carotenoids are biologically active compounds that are pigments in plants, microorganisms, fish, and birds, but they cannot be synthesized in animals. The absorption of carotenoids is not regulated when consumed by humans, so carotenoids in the blood and peripheral tissue reflect dietary intake.1 Vegetables and fruit contribute the overwhelming majority of carotenoids in the diet, so the amount of carotenoids in the circulation reflects vegetable and fruit intake, although a few influencing factors need to be considered in the interpretation of these concentrations as dietary biomarkers. Plasma carotenoids have been consistently associated with dietary intake of vegetables and fruit in observational studies,2,3 and tissue concentrations increase in response to feeding or prescribing these foods4-8 and in diet intervention studies that successfully promote increased vegetable and fruit intake.9-13
Breast cancer currently accounts for 32% of the incident cancers and 15% of the cancer deaths among women in the United States.14 The high incidence of breast cancer, combined with improvements in initial treatments, has resulted in a growing population of breast cancer survivors. Despite good short-term survival rates, women who have been diagnosed with breast cancer and have completed initial treatments remain at risk for recurrent cancer and are at higher risk for new primary breast cancers and early death than women who have not been diagnosed and treated for breast cancer.14,15 Whether diet plays a role in determining the likelihood of disease-free survival or mortality is a relevant issue in their medical management, because diet is something over which a woman can exert some control.
Compared with the amount of scientific effort that has been exerted to identify and characterize possible relationships between dietary factors and risk for primary breast cancer, relatively few studies have examined the relationship between these factors and disease-free survival in women who have been diagnosed and treated for breast cancer. The possibility that diet might influence risk for recurrence or mortality is feasible, on the basis of the numerous relevant biologic activities that are exhibited by various constituents of the diet.16 In eight of the 15 previous studies that have examined the association between diet and recurrence or survival after the diagnosis of breast cancer, intakes of vegetables, fruit, or nutrients that are indicative of consumption of these foods (eg, beta-carotene, vitamin C) have been examined (reviewed in Rock et al,17Goodwin et al,18and Borugian et al19). Three of these eight studies found a significant or marginally significant positive relationship with survival20-22; one reported that it identified a trend for this relationship23; and one found a protective effect among women with node-negative disease (62% of the total sample).24 Thus, four of the studies reported a protective effect, and four studies were null (although one of the latter studies found a protective effect in the largest subcategory of breast cancer). However, studies relying on self-reported dietary intake data are constrained by recognized limitations in the collection and interpretation of these data, even when the most rigorously developed methods are utilized.25,26
The purpose of this study was to examine the relationship between plasma total carotenoid concentration and risk for a new breast cancer event in a cohort of women who had been diagnosed with early-stage breast cancer and had completed initial treatments. Plasma carotenoids are a biomarker of vegetable and fruit intake, in addition to being a biologic indicator of exposure for these specific compounds at the tissue level. Inconsistencies in the results from previous studies of the relationship between dietary factors, especially vegetable and fruit intake, and risk for new or recurrent breast cancer justify the value and importance of undertaking this analysis at this time. The women in the cohort that is the focus of this study had been assigned to the control (nonintervention) group in the Women's Healthy Eating and Living (WHEL) study. As previously reported,27-29 women in the control group in that study did not change their diets after enrollment or in response to general activities involved in study participation. By examining the relationship between plasma carotenoids as an indicator of vegetable and fruit intake in this cohort, the present study adds to our knowledge of the relationship between dietary intake of these foods and recurrence-free survival following the diagnosis of breast cancer.
METHODS
Patients
Participants identified for this study were 1,551 women previously treated for breast cancer who were randomly assigned to the control arm of the WHEL study between March 1995 and November 2000. That study is testing whether diet modification can influence risk for recurrence and survival and is following women at risk for breast cancer recurrence; data on health status are collected at regular intervals. The WHEL study protocol, including selection criteria, data collection, and intervention methodology are provided elsewhere.30 Briefly, 3,088 women who were up to 4 years post-diagnosis and who had completed initial treatment for early-stage (stage I [ 1 cm], II or IIIA) breast cancer were enrolled. Approximately 40% of participants had been previously diagnosed with a stage I ( 1 cm) breast cancer, 55% with stage II, and 5% with stage IIIA, according to the accepted staging principles at the time of enrollment.31 Breast cancer stage was subsequently revised in accordance with more recent staging principles. Under the updated staging system, 45% of the study participants are stage II, and 15% are stage IIIA or IIIC.32 Recruitment took place at seven clinical sites in California, Oregon, Arizona, and Texas.
For the 1,551 women in the present study, the interval between initial cancer diagnosis and study enrollment varied from 6 to 48 months, with a mean of 24 months. Women had completed all initial treatments (eg, surgery, chemotherapy, radiation therapy) before enrollment in the study. In this cohort, 205 women had breast cancer recurrence or new primary breast cancer before July 31, 2004, that was medically confirmed by mid-November 2004. Thus, this data set provides the opportunity to adequately address the research question in a well-characterized cohort of women. Reporting of new breast cancer events and confirmations are ongoing for both study arms of the WHEL study, so the final breast cancer outcome for that study (which include the present cohort) will reflect an extended time period of follow-up.
Procedures
In the WHEL study, participants were randomly assigned to one of two study arms (control or intensive intervention), stratified by stage of disease, age at diagnosis, and clinic site. The control group comprises the cohort in the present study. As previously reported,27-29 dietary data and relevant biomarkers in these women in the control group indicated that they did not make significant changes in their diets as a result of study enrollment.
Dietary assessment in this study consisted of repeated 24-hour dietary recalls. Details regarding this dietary assessment methodology are described elsewhere.27,28 Briefly, each study participant provided four 24-hour dietary recalls including two weekdays and two weekend days over a 3-week period. Trained dietary assessors, who were blinded to the intervention or comparison group assignment of the participants, collected these data during telephone interviews. Nutrient calculations were performed using the Nutrition Data System for Research (NDS-R) software, developed by Nutrition Coordinating Center, University of Minnesota, Minneapolis, MN (Food and Nutrient Database 31, version 4.03, released November 2000).
Information about the use of dietary supplements was obtained from all participants at enrollment, and use is monitored throughout their involvement in the WHEL study, as previously reported.27,30 At the time of study enrollment, beta-carotene and lutein were the only carotenoids available from dietary supplements at dosages that would exert effects on plasma concentrations beyond the range of food sources ( 10 mg).1 Such levels could potentially influence the interpretation of plasma total carotenoid concentration as a biomarker of vegetable and fruit intake. Five women in the cohort that is the focus of the present study reported ingestion of > 10 mg/day lutein from dietary supplements, and 175 women reported ingestion of 10 mg/day beta-carotene from supplements, for a total of 11.6% of the sample being potentially affected by this consideration.
During the baseline clinic visit, a fasting blood sample was collected, height and weight were measured using standard procedures, and body mass index (BMI; weight[kg]/height[m2]) was computed. Blood samples collected at the clinic visit were immediately placed on ice, protected from light, and separated within one hour following collection, using centrifugation at 2,300x g at 4°C for 10 minutes. Plasma aliquots were stored at –80°C in cryogenic tubes until analysis. The institutional review boards of all the participating institutions approved procedures for this study, and written informed consent was obtained from all study participants before enrollment.
Analysis of Plasma Carotenoid and Cholesterol Concentrations
Plasma carotenoids, including alpha-carotene, beta-carotene, lutein, lycopene and beta-cryptoxanthin, were separated and quantified using a high-performance liquid chromatography (HPLC) method that has been previously described.33 Briefly, the HPLC analysis was conducted with a Varian Star 9010, 9050 system with variable wavelength UV/visible light detector (Varian Analytic Instruments, Walnut Creek, CA) with wavelength set at 450 nm. The mobile phase was acetonitrile/methanol/methylene chloride (70:10:30, v/v/v), with triethylamine (0.13 mL/L acetonitrile) and ammonium acetate (0.1 g/L methanol) modifiers used to enhance recovery. The column was a Supelco (Bellefonte, PA) Supelcosil LC-18 (25 cm x 4.6 mm x 5 μm). Zeaxanthin and lutein elute together with this analytic method, which quantifies > 90% of the carotenoids present in the circulation in humans. The variable described as plasma total carotenoids in the present study is the summed total of the quantified carotenoids. Accuracy was assessed by periodic analysis of National Institute of Standards and Technology (NIST) standard reference material, and a pooled plasma sample was analyzed with batches of study samples to monitor analytic precision, with a day-to-day coefficient of variation of approximately 7%. Also, the laboratory participates in the NIST round robin quality assurance program to monitor precision and reliability of these carotenoid measurements.
Total plasma cholesterol concentrations were determined with the Kodak Ektachem Analyzer system (Johnson & Johnson Clinical Diagnostics, Rochester, NY)34 and used in the interpretation of plasma carotenoid data. Carotenoids are transported in the plasma nonspecifically by cholesterol-rich lipoproteins, so the size of the pool in which these compounds exist in the circulation is a nondietary influencing factor that is considered in the analysis of the relationship between plasma carotenoid concentration (as an indicator of dietary intake) and recurrence-free survival.1 Standard reference materials from the manufacturer were used to validate analytic precision of these procedures. The laboratory also participates in the American College of Pathologists quality assurance program to monitor precision and reliability for these lipid measures.
Outcome Assessment
Breast cancer end points include the development of a new breast primary, contralateral breast primary, local/regional cancer recurrence, or distant recurrence/metastasis. The breast cancer event-free interval/survival was defined as the time from the date of initial breast cancer diagnosis to date of diagnosis of an additional breast cancer event, date of death from a cause other than breast cancer, or the earlier of July 31, 2004, and date of most recent semiannual telephone contact with WHEL study clinical site staff.
Outcome events were probed during semiannual interviews with study participants. These regular telephone interviews were conducted by the clinical site coordinator or designee and include probes for information on any hospitalization or medical diagnoses. Any reported recurrence or new primary cancer triggered a confirmation interview. Two independent oncologists reviewed medical records for all reported recurrences or new primary cancers. If disagreement occurred, the study pathologist from the WHEL study coordinating center adjudicated the outcome.
Statistical Analysis
Descriptive analysis and summary statistics were used to describe the study sample. The association between plasma carotenoid concentration and dietary carotenoid intake was modeled using a regression controlled for BMI, plasma cholesterol concentration, and smoking status. 2 tests were performed to examine associations between a new breast cancer event and tumor characteristics, adjuvant medical therapy, clinical site, patient age at initial cancer diagnosis, BMI, time interval between original breast cancer diagnosis and study entry, and family history of breast or ovarian cancer in first-degree relatives. To examine the relationship between baseline plasma total carotenoid concentration and time from diagnosis to recurrence or a new primary cancer, a delayed-entry Cox proportional hazards35 regression model was used. The delayed entry model adjusts for the fact that a woman who entered the WHEL study t years after the diagnosis of her original breast cancer was not under observation for a possible recurrence before t years.
Hazard ratio (HR) and 95% CI of recurrence-free survival for quartiles of baseline plasma carotenoids were computed, controlling for the varying interval between initial diagnosis and study entry, as well as covariates found to be significant (at the level .1) in the 2 analysis, including tumor stage, tumor grade, tumor estrogen and progesterone receptor status, chemotherapy, tamoxifen therapy, clinical site, and age at cancer diagnosis. BMI and plasma cholesterol concentration were also included in the Cox models, because these nondietary variables influence plasma carotenoid concentration.1 Further, BMI could affect risk for recurrence independent of other participant characteristics.17
Women without a new breast cancer event who had died were censored at their date of death; women without a new breast cancer event who had not died were censored July 31, 2004, or the date of their most recent semiannual call, whichever of the two dates came earlier. A recurrence-free survival graph showing the comparative hazards function per the Cox model for the four quartiles of baseline plasma carotenoid concentrations was prepared using mean values for continuous variables, and modal values for discrete variables. An illustration of this survival function is presented in this report for grade 2, stage II participants on tamoxifen. All analyses were conducted in SAS, version 8.1, 2000 (Cary, NC).
RESULTS
The median follow-up time after diagnosis for this cohort of women was 86 months (approximately 7 years). Mean dietary carotenoid consumption in this cohort was 13.74 mg/day (standard deviation [SD], 10.96 mg/day). A regression model for plasma carotenoid concentration revealed that the plasma concentration is indeed associated with dietary carotenoid intake (R2 = 0.28, P < .05), controlled for covariates. Table 1 summarizes breast cancer event status by participant and tumor characteristics. Tumor stage, grade, type, and estrogen and progesterone receptor status were significantly related to risk for recurrence or new primary cancer, as expected. Among women who had been diagnosed with a stage I cancer, 6.8% had a new breast cancer event, compared to 16.4% and 28.2% of the women diagnosed with stage II and IIIA breast cancer, respectively (P < .0001). Among women diagnosed with a grade 1 tumor, 5.7% had a new breast cancer event, compared with 12.4% and 17.1% of the women diagnosed with grade 2 and 3 cancer, respectively (P = .0005). Women who had been diagnosed with ductal and lobular cancer had approximately twice the rate of new cancer events (25.3%) as women with a history of lobular (not ductal) or ductal (not lobular) cancer, among whom the rates were 12.1% and 12.9%, respectively (P = .004). Across the categories of tumor hormone receptor status, women with estrogen receptor and progesterone receptor–positive tumors had the lowest frequency of new cancer events (11.2% v 13.2% to 17.9% for the other categories; P = .02).
Characteristics of treatment (adjuvant chemotherapy and tamoxifen therapy) also were significantly associated with risk for a new breast cancer event, although these characteristics would be expected to be determined in large part by the tumor stage, grade and type, as well as other factors. Younger women compared with older women (< 40 v 40 to 74 years of age) had a higher likelihood of a new breast cancer event. Among women in the younger age group, 18.6% had a new breast cancer event during the follow-up interval, compared with 12.6% of the older women (P = .03). The time interval between diagnosis and random assignment (< 2 years v 2 to 4 years) was marginally related to risk for recurrence or new primary cancer (P = .06), with the shorter time interval associated with higher risk for a new breast cancer event.
Table 2 shows the results of the Cox proportional hazards model for breast cancer end point in the study participants. As expected, tumor stage was directly associated with risk for a breast cancer end point (HR, 2.77; 95% CI, 1.89 to 4.06 for stage II; and HR, 5.31; 95% CI, 3.01 to 9.34 for stage IIIA, with stage I as reference). Tumor grade exhibited a similar relationship (HR, 2.11; 95% CI, 1.18 to 3.74 for grade 2; and HR, 2.49; 95% CI, 1.37 to 4.51 for grade 3, with grade 1 as reference). Treatment with tamoxifen was inversely associated with risk for a breast cancer end point (HR, 0.69; 95% CI, 0.49 to 0.97, with no tamoxifen treatment as reference).
Quartiles of plasma carotenoid concentration had average values of 1.038 umol/L (minimum [min], 0.268 umol/L; maximum [max], 1.392 umol/L) for the bottom quartile; 1.683 umol/L (min, 1.393 umol/L; max, 1.989 umol/L) for the second quartile; 2.375 umol/L (min, 1.989 umol/L; max, 2.863 umol/L) for the third quartile; and 4.189 umol/L (min, 2.867 umol/L; max, 22.920 umol/L) for the top quartile. In this model, women in the highest (v the lowest) quartile of plasma total carotenoid concentration had significantly reduced risk for recurrence (HR, 0.57; 95% CI 0.37 to 0.88). Women in the second and third quartiles of plasma total carotenoid concentration exhibited risks that were similar to each another. The point estimates for HR are < 1.0 for these quartiles, suggesting a protective effect compared to the lowest quartile. However, the 95% CIs are overlapping, indicating that there may be insufficient power to address whether the effect possibly follows a threshold or a dose-response pattern.
Figure 1 illustrates the results of the Cox proportional hazards model. The figure shows recurrence-free survival in years by quartile of baseline plasma carotenoid concentration, controlling for age at diagnosis, tumor hormone receptor status, adjuvant chemotherapy, clinical center, BMI, and plasma cholesterol concentration. This illustrative model assumes modal values so that the cancer is stage II, grade 2, and the participant was prescribed tamoxifen therapy.
We also conducted the analysis with the omission of data from the 180 women who had reported obtaining > 10 mg/day carotenoids from dietary supplements. The results of that analysis (data not shown) did not differ substantially from the results of the analysis that includes all of the participants. Higher plasma total carotenoid concentration was independently associated with reduced risk for a new breast cancer event.
DISCUSSION
We found plasma total carotenoid concentration to be inversely associated with risk for recurrence or new primary breast cancer in a cohort of 1,551 women who had been diagnosed with early stage breast cancer and who had completed initial treatments, when controlled for well-recognized factors that affect risk of recurrence and survival and other possible influencing factors. Being in the highest versus the lowest quartile of plasma total carotenoid concentration was associated with an estimated 43% reduction in risk for a new breast cancer event. Plasma carotenoids are a biologic marker of vegetable and fruit intake, so these results support the suggestion from prior studies, based on self-reported dietary intakes, that increased consumption of those foods may reduce the risk of recurrence or increase the likelihood of survival after the initial diagnosis and treatment of breast cancer.
As biologically active constituents of the diet, carotenoids exhibit several activities that could prevent or slow the progression of cancer, such as the inhibition of growth and malignant transformation and the promotion of apoptosis in transformed cells, similar to the effects of retinoids.1 However, an important consideration in the interpretation of observational studies that identify associations between carotenoid intakes (or tissue concentrations) and cancer is that these compounds reflect intake of vegetables and fruit, the major food sources of these compounds. These foods are complex, containing numerous constituents (in addition to carotenoids) that have biologic activities. Plasma carotenoids have been shown to be a dietary biomarker of vegetable and fruit intake, based on numerous feeding studies and diet modification efforts that have targeted groups over a wide range of demographic and other characteristics.4-13 Dietary supplements containing carotenoids also can contribute to the plasma concentration, but the carotenoid-containing supplements used by free-living individuals typically involve dosages that do not substantially affect the concentration in the circulation. In the present study, only a small minority of the participants reported use of dietary supplements containing carotenoids at a moderate or higher dosage that is beyond the amount available from food sources,1 and the direct relationship between plasma concentration and recurrence-free survival also was observed when those users were excluded.
The association between dietary intakes and recurrence or survival following the diagnosis of breast cancer has been examined in 15 studies published since 1985 (reviewed in Rock et al,17Goodwin et al,18and Borugian et al19). The patients examined and followed in those studies were cases who originally participated in case-control studies focused on primary breast cancer risk, were examined in clinical series, or were diagnosed with breast cancer while being followed within ongoing population-based observational studies or other established cohorts. A variety of approaches to diet assessment were used, involving self-reported dietary intakes before, during or after the diagnosis of breast cancer, and important nondietary factors known to influence recurrence or survival, such as stage at diagnosis, were not consistently considered in the analysis of associations. Five of the eight studies that examined intakes of vegetables, fruit or micronutrients reflecting intake of vegetables and fruit (eg, beta-carotene, vitamin C) found a direct association between consumption of these foods and survival, and the magnitude of the effect in those studies was a 20% to 90% reduction in risk for death in those with higher versus lower intakes.
Jain et al20 found a significantly lower risk of death with increased dietary beta-carotene (HR, 0.80; 95% CI, 0.65 to 0.99) and vitamin C (HR, 0.77; 95% CI, 0.62 to 0.95) intakes in 678 cases identified within the Canadian National Breast Screening Study cohort. Similarly, Ingram22 found a significantly decreased risk of death in women in the highest tertile of dietary beta-carotene, vitamin C, and fruit and vegetable intakes, although that analysis was not adjusted for stage of disease at diagnosis. In the study by Rohan et al,21 point estimates suggested that increased risk of death was associated with decreased beta-carotene intake (although nonsignificant, with P = .075 for trend), and Erwertz et al23 also reported a nonsignificant inverse association between vegetable consumption and risk of death. In the largest cohort to date in which diet and survival has been examined,24 a marginal protective effect of vegetable intake (relative risk, 0.62; 95% CI, 0.36 to 1.07; P = .02 for trend) was observed in women with node-negative breast cancer (1,237 of the 1,982 cases identified within the Nurses' Health Study cohort).
A well-recognized limitation of observational studies of the relationship between diet and risk for survival among women who have been diagnosed with cancer, or primary breast cancer risk, is the problem of imprecise methods that are used in the collection of dietary data.36 As observed in the present and previous studies,1 the amount of variability in plasma carotenoid concentration that can be explained by quantified dietary intake is not substantial. In addition to limitations in dietary assessment methodologies, factors such as the quality of the food content database (which is still quite limited for carotenoids) influence the strength of the association between intake and tissue level that is observed. Examining the association between breast cancer end point and plasma carotenoid concentration (versus dietary carotenoid intake) more accurately reflects true consumption and is a more biologically relevant approach if carotenoids are the focus of interest.
In previous studies that have examined the association between dietary factors and risk for primary breast cancer (rather than recurrence or a new cancer event), results based on dietary biomarkers have at times identified a stronger or different relationship than is evident in the analysis of self-reported intakes. For example, self-reported intake of vegetables and fruits was not significantly associated with risk for primary breast cancer in the New York University Women's Health Study,37 whereas serum carotenoid concentrations were significantly inversely associated with risk in that same cohort of women.38 Using suitable dietary biomarkers, rather than relying only on self-reported dietary intake data, is increasingly recognized as being of value in more accurately characterizing usual patterns of intake and true exposure.39 The present analysis, which is based on a dietary biomarker rather than self-reported dietary intake data, adds timely and valuable information to the knowledge base regarding the hypothesized relationship between diet and breast cancer risk.
In summary, results from the present study suggest that vegetable and fruit intake, as reflected in plasma total carotenoid concentration, may be associated with reduced risk for recurrence or new primary cancer in women who have been diagnosed and treated for breast cancer. A dietary pattern that includes a focus on eating vegetables and fruit has been associated with decreased risk of mortality from all causes in women40 and is recommended as a strategy for prevention of cardiovascular disease and control of hypertension as well.41 Thus, dietary guidance that promotes increased vegetable and fruit intake may be beneficial in the long-term management of the patient with a history of breast cancer, as efforts to identify how diet may specifically affect breast cancer mortality continue to move forward.
Appendix
The Women's Healthy Eating and Living Study Group: University of California, San Diego, Cancer Prevention and Control Program and Cancer Center, La Jolla, CA: John P. Pierce, PhD (Principal Investigator); Cheryl L. Rock, PhD, RD; Susan Faerber, BA; Vicky A. Newman, MS, RD; Shirley W. Flatt, MS; Sheila Kealey, MPH; Loki Natarajan, PhD; Barbara Parker, MD, Linda Wasserman, MD, PhD, Kathryn A. Hollenbach, PhD, Wayne A. Bardwell, PhD; Center for Health Research, Portland, OR: Njeri Karanja, PhD; Mark Rarick, MD; Kaiser Permanente Northern California, Oakland, CA: Bette J. Caan, DrPH; Lou Ferenbacher, MD; Stanford University/University of California, San Francisco, Palo Alto, CA: Marcia L. Stefanick, PhD; Robert Carlson, MD; University of Arizona, Tucson & Phoenix, AZ: Cynthia A. Thomson, PhD, RD; James Warnecke, MD; University of California, Davis, Davis, CA: Ellen B. Gold, PhD; Sidney Scudder, MD; The University of Texas M.D. Anderson Cancer Center, Houston, TX: Lovell A. Jones, PhD; Richard Theriault, DO. The authors also thank Dennis Heath, MS, and Mila Pruitt, for conducting the laboratory analysis of plasma carotenoid and cholesterol concentrations.
Authors' Disclosures of Potential Conflicts of Interest
The authors indicated no potential conflicts of interest.
NOTES
Supported by NCI Grant No. CA69375; University of California, San Diego, General Clinical Research Center NIH Grant No. M01-RR00827; University of California, San Francisco, General Clinical Research Center NIH Grant No. M01-RR00079; Stanford University General Clinical Research Center NIH Grant No. M01-RR00070; and the Walton Family Foundation.
Authors' disclosures of potential conflicts of interest are found at the end of this article.
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Prentice R: Dietary assessment and the reliability of nutritional epidemiology reports. Lancet 362:182-183, 2003
Kant AKI, Schatzkin A, Graubard BI, et al: A prospective study of diet quality and mortality in women. JAMA 283:2109-2115, 2000
Krauss RM, Eckel RH, Howard B, et al: AHA Dietary Guidelines revision 2000: A statement for healthcare professionals from the Nutrition Committee of the American Heart Association. Circulation 102:2284-2299, 2000(Cheryl L. Rock, Shirley W)
Division of Research, Kaiser Permanente Northern California, Oakland, CA
Arizona Cancer Center, University of Arizona, Tucson, AZ
M.D. Anderson Cancer Center, The University of Texas, Houston, TX
the Women's Healthy Eating and Living Study Group
ABSTRACT
PURPOSE: Previous studies suggest that diet may affect recurrence or survival rates in women who have been diagnosed with breast cancer. The purpose of this study was to examine the relationship between plasma carotenoid concentration, as a biomarker of vegetable and fruit intake, and risk for a new breast cancer event in a cohort of women with a history of early-stage breast cancer.
METHODS: Participants were 1,551 women previously treated for breast cancer who were randomly assigned to the control arm of a diet intervention trial between March 1995 and November 2000. Outcome events were probed during semiannual interviews and verified by medical record review. During the period under study, 205 women had a recurrence or new primary breast cancer. Plasma carotenoid concentrations were measured in baseline blood samples. Hazard ratios (HR) and 95% CIs by quartiles of plasma carotenoids were computed, controlling for tumor stage, grade, and hormone receptor status; chemotherapy and tamoxifen therapy; clinical site; age at diagnosis; body mass index; and plasma cholesterol concentration.
RESULTS: Women in the highest quartile of plasma total carotenoid concentration had significantly reduced risk for a new breast cancer event (HR, 0.57; 95% CI, 0.37 to 0.89), controlled for covariates influencing breast cancer prognosis.
CONCLUSION: Plasma carotenoids are a biologic marker of intake of vegetables and fruit, so this observation supports findings from previous studies that have linked increased vegetable and fruit intake with greater likelihood of recurrence-free survival in women who have been diagnosed with early-stage breast cancer.
INTRODUCTION
Carotenoids are biologically active compounds that are pigments in plants, microorganisms, fish, and birds, but they cannot be synthesized in animals. The absorption of carotenoids is not regulated when consumed by humans, so carotenoids in the blood and peripheral tissue reflect dietary intake.1 Vegetables and fruit contribute the overwhelming majority of carotenoids in the diet, so the amount of carotenoids in the circulation reflects vegetable and fruit intake, although a few influencing factors need to be considered in the interpretation of these concentrations as dietary biomarkers. Plasma carotenoids have been consistently associated with dietary intake of vegetables and fruit in observational studies,2,3 and tissue concentrations increase in response to feeding or prescribing these foods4-8 and in diet intervention studies that successfully promote increased vegetable and fruit intake.9-13
Breast cancer currently accounts for 32% of the incident cancers and 15% of the cancer deaths among women in the United States.14 The high incidence of breast cancer, combined with improvements in initial treatments, has resulted in a growing population of breast cancer survivors. Despite good short-term survival rates, women who have been diagnosed with breast cancer and have completed initial treatments remain at risk for recurrent cancer and are at higher risk for new primary breast cancers and early death than women who have not been diagnosed and treated for breast cancer.14,15 Whether diet plays a role in determining the likelihood of disease-free survival or mortality is a relevant issue in their medical management, because diet is something over which a woman can exert some control.
Compared with the amount of scientific effort that has been exerted to identify and characterize possible relationships between dietary factors and risk for primary breast cancer, relatively few studies have examined the relationship between these factors and disease-free survival in women who have been diagnosed and treated for breast cancer. The possibility that diet might influence risk for recurrence or mortality is feasible, on the basis of the numerous relevant biologic activities that are exhibited by various constituents of the diet.16 In eight of the 15 previous studies that have examined the association between diet and recurrence or survival after the diagnosis of breast cancer, intakes of vegetables, fruit, or nutrients that are indicative of consumption of these foods (eg, beta-carotene, vitamin C) have been examined (reviewed in Rock et al,17Goodwin et al,18and Borugian et al19). Three of these eight studies found a significant or marginally significant positive relationship with survival20-22; one reported that it identified a trend for this relationship23; and one found a protective effect among women with node-negative disease (62% of the total sample).24 Thus, four of the studies reported a protective effect, and four studies were null (although one of the latter studies found a protective effect in the largest subcategory of breast cancer). However, studies relying on self-reported dietary intake data are constrained by recognized limitations in the collection and interpretation of these data, even when the most rigorously developed methods are utilized.25,26
The purpose of this study was to examine the relationship between plasma total carotenoid concentration and risk for a new breast cancer event in a cohort of women who had been diagnosed with early-stage breast cancer and had completed initial treatments. Plasma carotenoids are a biomarker of vegetable and fruit intake, in addition to being a biologic indicator of exposure for these specific compounds at the tissue level. Inconsistencies in the results from previous studies of the relationship between dietary factors, especially vegetable and fruit intake, and risk for new or recurrent breast cancer justify the value and importance of undertaking this analysis at this time. The women in the cohort that is the focus of this study had been assigned to the control (nonintervention) group in the Women's Healthy Eating and Living (WHEL) study. As previously reported,27-29 women in the control group in that study did not change their diets after enrollment or in response to general activities involved in study participation. By examining the relationship between plasma carotenoids as an indicator of vegetable and fruit intake in this cohort, the present study adds to our knowledge of the relationship between dietary intake of these foods and recurrence-free survival following the diagnosis of breast cancer.
METHODS
Patients
Participants identified for this study were 1,551 women previously treated for breast cancer who were randomly assigned to the control arm of the WHEL study between March 1995 and November 2000. That study is testing whether diet modification can influence risk for recurrence and survival and is following women at risk for breast cancer recurrence; data on health status are collected at regular intervals. The WHEL study protocol, including selection criteria, data collection, and intervention methodology are provided elsewhere.30 Briefly, 3,088 women who were up to 4 years post-diagnosis and who had completed initial treatment for early-stage (stage I [ 1 cm], II or IIIA) breast cancer were enrolled. Approximately 40% of participants had been previously diagnosed with a stage I ( 1 cm) breast cancer, 55% with stage II, and 5% with stage IIIA, according to the accepted staging principles at the time of enrollment.31 Breast cancer stage was subsequently revised in accordance with more recent staging principles. Under the updated staging system, 45% of the study participants are stage II, and 15% are stage IIIA or IIIC.32 Recruitment took place at seven clinical sites in California, Oregon, Arizona, and Texas.
For the 1,551 women in the present study, the interval between initial cancer diagnosis and study enrollment varied from 6 to 48 months, with a mean of 24 months. Women had completed all initial treatments (eg, surgery, chemotherapy, radiation therapy) before enrollment in the study. In this cohort, 205 women had breast cancer recurrence or new primary breast cancer before July 31, 2004, that was medically confirmed by mid-November 2004. Thus, this data set provides the opportunity to adequately address the research question in a well-characterized cohort of women. Reporting of new breast cancer events and confirmations are ongoing for both study arms of the WHEL study, so the final breast cancer outcome for that study (which include the present cohort) will reflect an extended time period of follow-up.
Procedures
In the WHEL study, participants were randomly assigned to one of two study arms (control or intensive intervention), stratified by stage of disease, age at diagnosis, and clinic site. The control group comprises the cohort in the present study. As previously reported,27-29 dietary data and relevant biomarkers in these women in the control group indicated that they did not make significant changes in their diets as a result of study enrollment.
Dietary assessment in this study consisted of repeated 24-hour dietary recalls. Details regarding this dietary assessment methodology are described elsewhere.27,28 Briefly, each study participant provided four 24-hour dietary recalls including two weekdays and two weekend days over a 3-week period. Trained dietary assessors, who were blinded to the intervention or comparison group assignment of the participants, collected these data during telephone interviews. Nutrient calculations were performed using the Nutrition Data System for Research (NDS-R) software, developed by Nutrition Coordinating Center, University of Minnesota, Minneapolis, MN (Food and Nutrient Database 31, version 4.03, released November 2000).
Information about the use of dietary supplements was obtained from all participants at enrollment, and use is monitored throughout their involvement in the WHEL study, as previously reported.27,30 At the time of study enrollment, beta-carotene and lutein were the only carotenoids available from dietary supplements at dosages that would exert effects on plasma concentrations beyond the range of food sources ( 10 mg).1 Such levels could potentially influence the interpretation of plasma total carotenoid concentration as a biomarker of vegetable and fruit intake. Five women in the cohort that is the focus of the present study reported ingestion of > 10 mg/day lutein from dietary supplements, and 175 women reported ingestion of 10 mg/day beta-carotene from supplements, for a total of 11.6% of the sample being potentially affected by this consideration.
During the baseline clinic visit, a fasting blood sample was collected, height and weight were measured using standard procedures, and body mass index (BMI; weight[kg]/height[m2]) was computed. Blood samples collected at the clinic visit were immediately placed on ice, protected from light, and separated within one hour following collection, using centrifugation at 2,300x g at 4°C for 10 minutes. Plasma aliquots were stored at –80°C in cryogenic tubes until analysis. The institutional review boards of all the participating institutions approved procedures for this study, and written informed consent was obtained from all study participants before enrollment.
Analysis of Plasma Carotenoid and Cholesterol Concentrations
Plasma carotenoids, including alpha-carotene, beta-carotene, lutein, lycopene and beta-cryptoxanthin, were separated and quantified using a high-performance liquid chromatography (HPLC) method that has been previously described.33 Briefly, the HPLC analysis was conducted with a Varian Star 9010, 9050 system with variable wavelength UV/visible light detector (Varian Analytic Instruments, Walnut Creek, CA) with wavelength set at 450 nm. The mobile phase was acetonitrile/methanol/methylene chloride (70:10:30, v/v/v), with triethylamine (0.13 mL/L acetonitrile) and ammonium acetate (0.1 g/L methanol) modifiers used to enhance recovery. The column was a Supelco (Bellefonte, PA) Supelcosil LC-18 (25 cm x 4.6 mm x 5 μm). Zeaxanthin and lutein elute together with this analytic method, which quantifies > 90% of the carotenoids present in the circulation in humans. The variable described as plasma total carotenoids in the present study is the summed total of the quantified carotenoids. Accuracy was assessed by periodic analysis of National Institute of Standards and Technology (NIST) standard reference material, and a pooled plasma sample was analyzed with batches of study samples to monitor analytic precision, with a day-to-day coefficient of variation of approximately 7%. Also, the laboratory participates in the NIST round robin quality assurance program to monitor precision and reliability of these carotenoid measurements.
Total plasma cholesterol concentrations were determined with the Kodak Ektachem Analyzer system (Johnson & Johnson Clinical Diagnostics, Rochester, NY)34 and used in the interpretation of plasma carotenoid data. Carotenoids are transported in the plasma nonspecifically by cholesterol-rich lipoproteins, so the size of the pool in which these compounds exist in the circulation is a nondietary influencing factor that is considered in the analysis of the relationship between plasma carotenoid concentration (as an indicator of dietary intake) and recurrence-free survival.1 Standard reference materials from the manufacturer were used to validate analytic precision of these procedures. The laboratory also participates in the American College of Pathologists quality assurance program to monitor precision and reliability for these lipid measures.
Outcome Assessment
Breast cancer end points include the development of a new breast primary, contralateral breast primary, local/regional cancer recurrence, or distant recurrence/metastasis. The breast cancer event-free interval/survival was defined as the time from the date of initial breast cancer diagnosis to date of diagnosis of an additional breast cancer event, date of death from a cause other than breast cancer, or the earlier of July 31, 2004, and date of most recent semiannual telephone contact with WHEL study clinical site staff.
Outcome events were probed during semiannual interviews with study participants. These regular telephone interviews were conducted by the clinical site coordinator or designee and include probes for information on any hospitalization or medical diagnoses. Any reported recurrence or new primary cancer triggered a confirmation interview. Two independent oncologists reviewed medical records for all reported recurrences or new primary cancers. If disagreement occurred, the study pathologist from the WHEL study coordinating center adjudicated the outcome.
Statistical Analysis
Descriptive analysis and summary statistics were used to describe the study sample. The association between plasma carotenoid concentration and dietary carotenoid intake was modeled using a regression controlled for BMI, plasma cholesterol concentration, and smoking status. 2 tests were performed to examine associations between a new breast cancer event and tumor characteristics, adjuvant medical therapy, clinical site, patient age at initial cancer diagnosis, BMI, time interval between original breast cancer diagnosis and study entry, and family history of breast or ovarian cancer in first-degree relatives. To examine the relationship between baseline plasma total carotenoid concentration and time from diagnosis to recurrence or a new primary cancer, a delayed-entry Cox proportional hazards35 regression model was used. The delayed entry model adjusts for the fact that a woman who entered the WHEL study t years after the diagnosis of her original breast cancer was not under observation for a possible recurrence before t years.
Hazard ratio (HR) and 95% CI of recurrence-free survival for quartiles of baseline plasma carotenoids were computed, controlling for the varying interval between initial diagnosis and study entry, as well as covariates found to be significant (at the level .1) in the 2 analysis, including tumor stage, tumor grade, tumor estrogen and progesterone receptor status, chemotherapy, tamoxifen therapy, clinical site, and age at cancer diagnosis. BMI and plasma cholesterol concentration were also included in the Cox models, because these nondietary variables influence plasma carotenoid concentration.1 Further, BMI could affect risk for recurrence independent of other participant characteristics.17
Women without a new breast cancer event who had died were censored at their date of death; women without a new breast cancer event who had not died were censored July 31, 2004, or the date of their most recent semiannual call, whichever of the two dates came earlier. A recurrence-free survival graph showing the comparative hazards function per the Cox model for the four quartiles of baseline plasma carotenoid concentrations was prepared using mean values for continuous variables, and modal values for discrete variables. An illustration of this survival function is presented in this report for grade 2, stage II participants on tamoxifen. All analyses were conducted in SAS, version 8.1, 2000 (Cary, NC).
RESULTS
The median follow-up time after diagnosis for this cohort of women was 86 months (approximately 7 years). Mean dietary carotenoid consumption in this cohort was 13.74 mg/day (standard deviation [SD], 10.96 mg/day). A regression model for plasma carotenoid concentration revealed that the plasma concentration is indeed associated with dietary carotenoid intake (R2 = 0.28, P < .05), controlled for covariates. Table 1 summarizes breast cancer event status by participant and tumor characteristics. Tumor stage, grade, type, and estrogen and progesterone receptor status were significantly related to risk for recurrence or new primary cancer, as expected. Among women who had been diagnosed with a stage I cancer, 6.8% had a new breast cancer event, compared to 16.4% and 28.2% of the women diagnosed with stage II and IIIA breast cancer, respectively (P < .0001). Among women diagnosed with a grade 1 tumor, 5.7% had a new breast cancer event, compared with 12.4% and 17.1% of the women diagnosed with grade 2 and 3 cancer, respectively (P = .0005). Women who had been diagnosed with ductal and lobular cancer had approximately twice the rate of new cancer events (25.3%) as women with a history of lobular (not ductal) or ductal (not lobular) cancer, among whom the rates were 12.1% and 12.9%, respectively (P = .004). Across the categories of tumor hormone receptor status, women with estrogen receptor and progesterone receptor–positive tumors had the lowest frequency of new cancer events (11.2% v 13.2% to 17.9% for the other categories; P = .02).
Characteristics of treatment (adjuvant chemotherapy and tamoxifen therapy) also were significantly associated with risk for a new breast cancer event, although these characteristics would be expected to be determined in large part by the tumor stage, grade and type, as well as other factors. Younger women compared with older women (< 40 v 40 to 74 years of age) had a higher likelihood of a new breast cancer event. Among women in the younger age group, 18.6% had a new breast cancer event during the follow-up interval, compared with 12.6% of the older women (P = .03). The time interval between diagnosis and random assignment (< 2 years v 2 to 4 years) was marginally related to risk for recurrence or new primary cancer (P = .06), with the shorter time interval associated with higher risk for a new breast cancer event.
Table 2 shows the results of the Cox proportional hazards model for breast cancer end point in the study participants. As expected, tumor stage was directly associated with risk for a breast cancer end point (HR, 2.77; 95% CI, 1.89 to 4.06 for stage II; and HR, 5.31; 95% CI, 3.01 to 9.34 for stage IIIA, with stage I as reference). Tumor grade exhibited a similar relationship (HR, 2.11; 95% CI, 1.18 to 3.74 for grade 2; and HR, 2.49; 95% CI, 1.37 to 4.51 for grade 3, with grade 1 as reference). Treatment with tamoxifen was inversely associated with risk for a breast cancer end point (HR, 0.69; 95% CI, 0.49 to 0.97, with no tamoxifen treatment as reference).
Quartiles of plasma carotenoid concentration had average values of 1.038 umol/L (minimum [min], 0.268 umol/L; maximum [max], 1.392 umol/L) for the bottom quartile; 1.683 umol/L (min, 1.393 umol/L; max, 1.989 umol/L) for the second quartile; 2.375 umol/L (min, 1.989 umol/L; max, 2.863 umol/L) for the third quartile; and 4.189 umol/L (min, 2.867 umol/L; max, 22.920 umol/L) for the top quartile. In this model, women in the highest (v the lowest) quartile of plasma total carotenoid concentration had significantly reduced risk for recurrence (HR, 0.57; 95% CI 0.37 to 0.88). Women in the second and third quartiles of plasma total carotenoid concentration exhibited risks that were similar to each another. The point estimates for HR are < 1.0 for these quartiles, suggesting a protective effect compared to the lowest quartile. However, the 95% CIs are overlapping, indicating that there may be insufficient power to address whether the effect possibly follows a threshold or a dose-response pattern.
Figure 1 illustrates the results of the Cox proportional hazards model. The figure shows recurrence-free survival in years by quartile of baseline plasma carotenoid concentration, controlling for age at diagnosis, tumor hormone receptor status, adjuvant chemotherapy, clinical center, BMI, and plasma cholesterol concentration. This illustrative model assumes modal values so that the cancer is stage II, grade 2, and the participant was prescribed tamoxifen therapy.
We also conducted the analysis with the omission of data from the 180 women who had reported obtaining > 10 mg/day carotenoids from dietary supplements. The results of that analysis (data not shown) did not differ substantially from the results of the analysis that includes all of the participants. Higher plasma total carotenoid concentration was independently associated with reduced risk for a new breast cancer event.
DISCUSSION
We found plasma total carotenoid concentration to be inversely associated with risk for recurrence or new primary breast cancer in a cohort of 1,551 women who had been diagnosed with early stage breast cancer and who had completed initial treatments, when controlled for well-recognized factors that affect risk of recurrence and survival and other possible influencing factors. Being in the highest versus the lowest quartile of plasma total carotenoid concentration was associated with an estimated 43% reduction in risk for a new breast cancer event. Plasma carotenoids are a biologic marker of vegetable and fruit intake, so these results support the suggestion from prior studies, based on self-reported dietary intakes, that increased consumption of those foods may reduce the risk of recurrence or increase the likelihood of survival after the initial diagnosis and treatment of breast cancer.
As biologically active constituents of the diet, carotenoids exhibit several activities that could prevent or slow the progression of cancer, such as the inhibition of growth and malignant transformation and the promotion of apoptosis in transformed cells, similar to the effects of retinoids.1 However, an important consideration in the interpretation of observational studies that identify associations between carotenoid intakes (or tissue concentrations) and cancer is that these compounds reflect intake of vegetables and fruit, the major food sources of these compounds. These foods are complex, containing numerous constituents (in addition to carotenoids) that have biologic activities. Plasma carotenoids have been shown to be a dietary biomarker of vegetable and fruit intake, based on numerous feeding studies and diet modification efforts that have targeted groups over a wide range of demographic and other characteristics.4-13 Dietary supplements containing carotenoids also can contribute to the plasma concentration, but the carotenoid-containing supplements used by free-living individuals typically involve dosages that do not substantially affect the concentration in the circulation. In the present study, only a small minority of the participants reported use of dietary supplements containing carotenoids at a moderate or higher dosage that is beyond the amount available from food sources,1 and the direct relationship between plasma concentration and recurrence-free survival also was observed when those users were excluded.
The association between dietary intakes and recurrence or survival following the diagnosis of breast cancer has been examined in 15 studies published since 1985 (reviewed in Rock et al,17Goodwin et al,18and Borugian et al19). The patients examined and followed in those studies were cases who originally participated in case-control studies focused on primary breast cancer risk, were examined in clinical series, or were diagnosed with breast cancer while being followed within ongoing population-based observational studies or other established cohorts. A variety of approaches to diet assessment were used, involving self-reported dietary intakes before, during or after the diagnosis of breast cancer, and important nondietary factors known to influence recurrence or survival, such as stage at diagnosis, were not consistently considered in the analysis of associations. Five of the eight studies that examined intakes of vegetables, fruit or micronutrients reflecting intake of vegetables and fruit (eg, beta-carotene, vitamin C) found a direct association between consumption of these foods and survival, and the magnitude of the effect in those studies was a 20% to 90% reduction in risk for death in those with higher versus lower intakes.
Jain et al20 found a significantly lower risk of death with increased dietary beta-carotene (HR, 0.80; 95% CI, 0.65 to 0.99) and vitamin C (HR, 0.77; 95% CI, 0.62 to 0.95) intakes in 678 cases identified within the Canadian National Breast Screening Study cohort. Similarly, Ingram22 found a significantly decreased risk of death in women in the highest tertile of dietary beta-carotene, vitamin C, and fruit and vegetable intakes, although that analysis was not adjusted for stage of disease at diagnosis. In the study by Rohan et al,21 point estimates suggested that increased risk of death was associated with decreased beta-carotene intake (although nonsignificant, with P = .075 for trend), and Erwertz et al23 also reported a nonsignificant inverse association between vegetable consumption and risk of death. In the largest cohort to date in which diet and survival has been examined,24 a marginal protective effect of vegetable intake (relative risk, 0.62; 95% CI, 0.36 to 1.07; P = .02 for trend) was observed in women with node-negative breast cancer (1,237 of the 1,982 cases identified within the Nurses' Health Study cohort).
A well-recognized limitation of observational studies of the relationship between diet and risk for survival among women who have been diagnosed with cancer, or primary breast cancer risk, is the problem of imprecise methods that are used in the collection of dietary data.36 As observed in the present and previous studies,1 the amount of variability in plasma carotenoid concentration that can be explained by quantified dietary intake is not substantial. In addition to limitations in dietary assessment methodologies, factors such as the quality of the food content database (which is still quite limited for carotenoids) influence the strength of the association between intake and tissue level that is observed. Examining the association between breast cancer end point and plasma carotenoid concentration (versus dietary carotenoid intake) more accurately reflects true consumption and is a more biologically relevant approach if carotenoids are the focus of interest.
In previous studies that have examined the association between dietary factors and risk for primary breast cancer (rather than recurrence or a new cancer event), results based on dietary biomarkers have at times identified a stronger or different relationship than is evident in the analysis of self-reported intakes. For example, self-reported intake of vegetables and fruits was not significantly associated with risk for primary breast cancer in the New York University Women's Health Study,37 whereas serum carotenoid concentrations were significantly inversely associated with risk in that same cohort of women.38 Using suitable dietary biomarkers, rather than relying only on self-reported dietary intake data, is increasingly recognized as being of value in more accurately characterizing usual patterns of intake and true exposure.39 The present analysis, which is based on a dietary biomarker rather than self-reported dietary intake data, adds timely and valuable information to the knowledge base regarding the hypothesized relationship between diet and breast cancer risk.
In summary, results from the present study suggest that vegetable and fruit intake, as reflected in plasma total carotenoid concentration, may be associated with reduced risk for recurrence or new primary cancer in women who have been diagnosed and treated for breast cancer. A dietary pattern that includes a focus on eating vegetables and fruit has been associated with decreased risk of mortality from all causes in women40 and is recommended as a strategy for prevention of cardiovascular disease and control of hypertension as well.41 Thus, dietary guidance that promotes increased vegetable and fruit intake may be beneficial in the long-term management of the patient with a history of breast cancer, as efforts to identify how diet may specifically affect breast cancer mortality continue to move forward.
Appendix
The Women's Healthy Eating and Living Study Group: University of California, San Diego, Cancer Prevention and Control Program and Cancer Center, La Jolla, CA: John P. Pierce, PhD (Principal Investigator); Cheryl L. Rock, PhD, RD; Susan Faerber, BA; Vicky A. Newman, MS, RD; Shirley W. Flatt, MS; Sheila Kealey, MPH; Loki Natarajan, PhD; Barbara Parker, MD, Linda Wasserman, MD, PhD, Kathryn A. Hollenbach, PhD, Wayne A. Bardwell, PhD; Center for Health Research, Portland, OR: Njeri Karanja, PhD; Mark Rarick, MD; Kaiser Permanente Northern California, Oakland, CA: Bette J. Caan, DrPH; Lou Ferenbacher, MD; Stanford University/University of California, San Francisco, Palo Alto, CA: Marcia L. Stefanick, PhD; Robert Carlson, MD; University of Arizona, Tucson & Phoenix, AZ: Cynthia A. Thomson, PhD, RD; James Warnecke, MD; University of California, Davis, Davis, CA: Ellen B. Gold, PhD; Sidney Scudder, MD; The University of Texas M.D. Anderson Cancer Center, Houston, TX: Lovell A. Jones, PhD; Richard Theriault, DO. The authors also thank Dennis Heath, MS, and Mila Pruitt, for conducting the laboratory analysis of plasma carotenoid and cholesterol concentrations.
Authors' Disclosures of Potential Conflicts of Interest
The authors indicated no potential conflicts of interest.
NOTES
Supported by NCI Grant No. CA69375; University of California, San Diego, General Clinical Research Center NIH Grant No. M01-RR00827; University of California, San Francisco, General Clinical Research Center NIH Grant No. M01-RR00079; Stanford University General Clinical Research Center NIH Grant No. M01-RR00070; and the Walton Family Foundation.
Authors' disclosures of potential conflicts of interest are found at the end of this article.
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