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Soy Food Intake and Breast Cancer Survival
breast cancer as well as a 34% lower risk of lobular breast cancer. When they examined food groups rich in fiber, no single food group was associated with risk. The source of fiber values for the analysis came from a nutrient database that did not include updated information on fiber concentrations in foods.1 If one identifies the food contributors to soluble fiber intake, the major contributors are psyllium husk (eg, Metamucil), oat bran, prunes and plums, peas, and pinto beans. These major food contributors do not fall into 1 particular food group that could be identified for a dietary food group intervention strategy. This study by Park and colleagues is 1 of only 3 studies that examine the role of diet in breast cancer by tumor subtype.2,3 All these studies found that a dietary component or pattern
influences the risk of ER /PR tumor subtypes but not ER+/PR+ tumor subtypes, but each study had a different dietary tool and a different study design or analysis; therefore, it is not possible to determine an evidence-based ranking of the results reported here by Park and colleagues. Future research on diet and breast cancer tumor subtype would benefit from the use of a comparable dietary tool, use of a food composition database with more comprehensive and updated fiber values, and identification of lifetime dietary intakes because the reported periods of dietary intake in the cited studies may be too brief to influence breast cancer risk.
Soy Food Intake and Breast Cancer Survival
Design, Setting, and Participants.—The Shanghai Breast Cancer Survival Study, a large, populationbased cohort study of 5042 female breast cancer survivors in China. Women aged 20 to 75 years with diagnoses between March 2002 and April 2006 were recruited and followed up through June 2009. Information on cancer diagnosis and treatment, lifestyle exposures after cancer diagnosis, and disease progression was collected at approximately 6 months after cancer diagnosis and was reassessed at 3 follow-up interviews conducted at 18, 36, and 60 months after diagnosis. Annual record linkage with the Shanghai Vital Statistics Registry database was carried out to obtain survival information for participants who were lost to follow-up. Medical charts were
Shu XO, Zheng Y, Cai H, et al (Vanderbilt Univ Med Ctr, Nashville, TN; Shanghai Inst of Preventive Medicine, China) JAMA 302:2437-2443, 2009
Context.—Soy foods are rich in isoflavones, a major group of phytoestrogens that have been hypothesized to reduce the risk of breast cancer. However, the estrogen-like effect of isoflavones and the potential interaction between isoflavones and tamoxifen have led to concern about soy food consumption among breast cancer patients. Objective.—To evaluate the association of soy food intake after diagnosis of breast cancer with total mortality and cancer recurrence.
References 1. Li BW, Andrews KW, Pehrsson PR. Individual sugars, soluble, and insoluble dietary fiber contents of 70 high consumption foods. J Food Compos Anal. 2002;15:715-723. 2. Chlebowski RT, Blackburn GL, Thomson CA, et al. Dietary fat reduction and breast cancer outcome: interim efficacy results from the Women’s Intervention Nutrition Study. J Natl Cancer Inst. 2006;98: 1767-1776. 3. Fung TT, Hu FB, McCullough ML, Newby PK, Willett WC, Holmes MD. Diet quality is associated with the risk of estrogen receptor-negative breast cancer in postmenopausal women. J Nutr. 2006;136:466-472.
M. R. Forman, PhD L. M. Hernandez, PhD
reviewed to verify disease and treatment information. Main Outcome Measures.—Total mortality and breast cancer recurrence or breast cancer–related deaths. Cox regression analysis was carried out with adjustment for known clinical predictors and other lifestyle factors. Soy food intake was treated as a timedependent variable. Results.—During the median follow-up of 3.9 years (range, 0.5-6.2 years), 444 deaths and 534 recurrences or breast cancer–related deaths were documented in 5033 surgically treated breast cancer patients. Soy food intake, as measured by either soy protein or soy isoflavone intake, was inversely associated with mortality and recurrence. The hazard ratio associated with the highest quartile of soy protein
Breast Diseases: A Year BookÒ Quarterly Vol 21 No 2 2010
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intake was 0.71 (95% confidence interval [CI], 0.54-0.92) for total mortality and 0.68 (95% CI, 0.540.87) for recurrence compared with the lowest quartile of intake. The multivariate-adjusted 4-year mortality rates were 10.3% and 7.4%, and the 4-year recurrence rates were 11.2% and 8.0%, respectively, for women in the lowest and highest quartiles of soy protein intake. The inverse association was evident among women with either estrogen receptor–positive or –negative breast cancer and was present in both users and nonusers of tamoxifen. Conclusion.—Among women with breast cancer, soy food consumption was significantly associated with decreased risk of death and recurrence. Growing evidence shows a link between lifestyle behaviors, such as diet, and clinical outcomes for both cancer prevention and survivorship. Cancer patients often take herbs and supplements with the hope of improving their outcomes, and breast cancer patients in particular have been documented to commonly utilize complementary and alternative medicine.1,2 One controversial topic remains: the ingestion of soy and its related products. Natural soy is known to contain phytoestrogens, such as isoflavones, and these compounds have been shown in preclinical studies to promote estrogen-dependent breast cancer growth.3 Thus, breast cancer patients are commonly advised to avoid all dietary soy.
124
This JAMA article by Shu and colleagues investigated the association between soy food intake and breast cancer survival among a prospective, population-based cohort of more than 5000 Chinese women diagnosed with breast cancer between 2002 and 2006. In-person interviews were conducted at baseline, 18 months, and 36 months after cancer diagnosis about food consumption, including soy. After an approximate median follow-up of 4 years, soy food intake was inversely associated with breast cancer recurrence and mortality (ie, high soy intake was associated with increased survival). Multivariate-adjusted 4-year mortality and recurrence rates were 10.3% versus 7.4% and 11.2% versus 8.0%, respectively, for women in the lowest and highest quartiles of soy protein intake. This finding generally remained in comparisons of estrogen receptor–positive/negative and tamoxifen user/nonuser subgroups. This study by Shu and colleagues provides further evidence that regular dietary soy as part of a normal diet is safe. Additionally, the inverse association between soy intake and cancer recurrence and breast cancer– specific mortality indicates a possible beneficial effect, which appears to be proportional to the amount of soy intake. This study and others4 create a growing body of evidence that the current advice that all soy foods should be removed from a normal diet should be questioned. The role of nondietary soy products, such as soy
Breast Diseases: A Year BookÒ Quarterly Vol 21 No 2 2010
supplements, powders, or pills, and heavily processed soy items, such as soy cheese, soy hot dogs, or soy turkey, remains unclear; thus, these products should be avoided. Future randomized trials are needed to verify whether dietary soy truly confers a beneficial effect. R. T. Lee, MD L. Cohen, PhD
References 1. Astin JA, Reilly C, Perkins C, Child WL; Susan G. Komen Breast Cancer Foundation. Breast cancer patients’ perspectives on and use of complementary and alternative medicine: a study by the Susan G. Komen Breast Cancer Foundation. J Soc Integr Oncol. 2006;4:157-169. 2. DiGianni LM, Garber JE, Winer EP. Complementary and alternative medicine use among women with breast cancer. J Clin Oncol. 2002;20: 34S-38S. 3. Helferich WG, Andrade JE, Hoagland MS. Phytoestrogens and breast cancer: a complex story. Inflammopharmacology. 2008;16: 219-226. 4. Guha N, Kwan ML, Quesenberry CP Jr, Weltzien EK, Castillo AL, Caan BJ. Soy isoflavones and risk of cancer recurrence in a cohort of breast cancer survivors: the Life After Cancer Epidemiology study. Breast Cancer Res Treat. 2009; 118:395-405.
influences the risk of ER /PR tumor subtypes but not ER+/PR+ tumor subtypes, but each study had a different dietary tool and a different study design or analysis; therefore, it is not possible to determine an evidence-based ranking of the results reported here by Park and colleagues. Future research on diet and breast cancer tumor subtype would benefit from the use of a comparable dietary tool, use of a food composition database with more comprehensive and updated fiber values, and identification of lifetime dietary intakes because the reported periods of dietary intake in the cited studies may be too brief to influence breast cancer risk.
Soy Food Intake and Breast Cancer Survival
Design, Setting, and Participants.—The Shanghai Breast Cancer Survival Study, a large, populationbased cohort study of 5042 female breast cancer survivors in China. Women aged 20 to 75 years with diagnoses between March 2002 and April 2006 were recruited and followed up through June 2009. Information on cancer diagnosis and treatment, lifestyle exposures after cancer diagnosis, and disease progression was collected at approximately 6 months after cancer diagnosis and was reassessed at 3 follow-up interviews conducted at 18, 36, and 60 months after diagnosis. Annual record linkage with the Shanghai Vital Statistics Registry database was carried out to obtain survival information for participants who were lost to follow-up. Medical charts were
Shu XO, Zheng Y, Cai H, et al (Vanderbilt Univ Med Ctr, Nashville, TN; Shanghai Inst of Preventive Medicine, China) JAMA 302:2437-2443, 2009
Context.—Soy foods are rich in isoflavones, a major group of phytoestrogens that have been hypothesized to reduce the risk of breast cancer. However, the estrogen-like effect of isoflavones and the potential interaction between isoflavones and tamoxifen have led to concern about soy food consumption among breast cancer patients. Objective.—To evaluate the association of soy food intake after diagnosis of breast cancer with total mortality and cancer recurrence.
References 1. Li BW, Andrews KW, Pehrsson PR. Individual sugars, soluble, and insoluble dietary fiber contents of 70 high consumption foods. J Food Compos Anal. 2002;15:715-723. 2. Chlebowski RT, Blackburn GL, Thomson CA, et al. Dietary fat reduction and breast cancer outcome: interim efficacy results from the Women’s Intervention Nutrition Study. J Natl Cancer Inst. 2006;98: 1767-1776. 3. Fung TT, Hu FB, McCullough ML, Newby PK, Willett WC, Holmes MD. Diet quality is associated with the risk of estrogen receptor-negative breast cancer in postmenopausal women. J Nutr. 2006;136:466-472.
M. R. Forman, PhD L. M. Hernandez, PhD
reviewed to verify disease and treatment information. Main Outcome Measures.—Total mortality and breast cancer recurrence or breast cancer–related deaths. Cox regression analysis was carried out with adjustment for known clinical predictors and other lifestyle factors. Soy food intake was treated as a timedependent variable. Results.—During the median follow-up of 3.9 years (range, 0.5-6.2 years), 444 deaths and 534 recurrences or breast cancer–related deaths were documented in 5033 surgically treated breast cancer patients. Soy food intake, as measured by either soy protein or soy isoflavone intake, was inversely associated with mortality and recurrence. The hazard ratio associated with the highest quartile of soy protein
Breast Diseases: A Year BookÒ Quarterly Vol 21 No 2 2010
123
intake was 0.71 (95% confidence interval [CI], 0.54-0.92) for total mortality and 0.68 (95% CI, 0.540.87) for recurrence compared with the lowest quartile of intake. The multivariate-adjusted 4-year mortality rates were 10.3% and 7.4%, and the 4-year recurrence rates were 11.2% and 8.0%, respectively, for women in the lowest and highest quartiles of soy protein intake. The inverse association was evident among women with either estrogen receptor–positive or –negative breast cancer and was present in both users and nonusers of tamoxifen. Conclusion.—Among women with breast cancer, soy food consumption was significantly associated with decreased risk of death and recurrence. Growing evidence shows a link between lifestyle behaviors, such as diet, and clinical outcomes for both cancer prevention and survivorship. Cancer patients often take herbs and supplements with the hope of improving their outcomes, and breast cancer patients in particular have been documented to commonly utilize complementary and alternative medicine.1,2 One controversial topic remains: the ingestion of soy and its related products. Natural soy is known to contain phytoestrogens, such as isoflavones, and these compounds have been shown in preclinical studies to promote estrogen-dependent breast cancer growth.3 Thus, breast cancer patients are commonly advised to avoid all dietary soy.
124
This JAMA article by Shu and colleagues investigated the association between soy food intake and breast cancer survival among a prospective, population-based cohort of more than 5000 Chinese women diagnosed with breast cancer between 2002 and 2006. In-person interviews were conducted at baseline, 18 months, and 36 months after cancer diagnosis about food consumption, including soy. After an approximate median follow-up of 4 years, soy food intake was inversely associated with breast cancer recurrence and mortality (ie, high soy intake was associated with increased survival). Multivariate-adjusted 4-year mortality and recurrence rates were 10.3% versus 7.4% and 11.2% versus 8.0%, respectively, for women in the lowest and highest quartiles of soy protein intake. This finding generally remained in comparisons of estrogen receptor–positive/negative and tamoxifen user/nonuser subgroups. This study by Shu and colleagues provides further evidence that regular dietary soy as part of a normal diet is safe. Additionally, the inverse association between soy intake and cancer recurrence and breast cancer– specific mortality indicates a possible beneficial effect, which appears to be proportional to the amount of soy intake. This study and others4 create a growing body of evidence that the current advice that all soy foods should be removed from a normal diet should be questioned. The role of nondietary soy products, such as soy
Breast Diseases: A Year BookÒ Quarterly Vol 21 No 2 2010
supplements, powders, or pills, and heavily processed soy items, such as soy cheese, soy hot dogs, or soy turkey, remains unclear; thus, these products should be avoided. Future randomized trials are needed to verify whether dietary soy truly confers a beneficial effect. R. T. Lee, MD L. Cohen, PhD
References 1. Astin JA, Reilly C, Perkins C, Child WL; Susan G. Komen Breast Cancer Foundation. Breast cancer patients’ perspectives on and use of complementary and alternative medicine: a study by the Susan G. Komen Breast Cancer Foundation. J Soc Integr Oncol. 2006;4:157-169. 2. DiGianni LM, Garber JE, Winer EP. Complementary and alternative medicine use among women with breast cancer. J Clin Oncol. 2002;20: 34S-38S. 3. Helferich WG, Andrade JE, Hoagland MS. Phytoestrogens and breast cancer: a complex story. Inflammopharmacology. 2008;16: 219-226. 4. Guha N, Kwan ML, Quesenberry CP Jr, Weltzien EK, Castillo AL, Caan BJ. Soy isoflavones and risk of cancer recurrence in a cohort of breast cancer survivors: the Life After Cancer Epidemiology study. Breast Cancer Res Treat. 2009; 118:395-405.