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. 2009 Dec 9;302(22):2437-43.
doi: 10.1001/jama.2009.1783.

Soy food intake and breast cancer survival

Xiao Ou Shu  1 , Ying Zheng, Hui Cai, Kai Gu, Zhi Chen, Wei Zheng, Wei Lu
Affiliations

Soy food intake and breast cancer survival

Xiao Ou Shu et al. JAMA. .

Abstract

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.

Design, setting, and participants: The Shanghai Breast Cancer Survival Study, a large, population-based 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 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 time-dependent 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 intake was 0.71 (95% confidence interval [CI], 0.54-0.92) for total mortality and 0.68 (95% CI, 0.54-0.87) 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.

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Conflict of interest statement

Conflicts of Interest: XOS received a small research development fund from the United Soybean Board in 2005. The United Soybean Board played no role in the design, implementation, or result interpretation of this study or in the preparation or approval of the manuscript. No other authors have any conflicts of interest to declare.

Figures

Figure 1
Figure 1. Shanghai Breast Cancer Survival Study Case Recruitment and Follow-up
Figure 2
Figure 2. Association Pattern for Soy Protein Intake and Breast Cancer Outcomes
Figure 3
Figure 3. Association Pattern for Soy Isoflavone Intake an Breast Cancer Outcomes
Figure 4
Figure 4. Total Mortality by Soy Protein Intake
Figure 5
Figure 5. Breast Cancer Recurrence by Soy Protein Intake
See this image and copyright information in PMC

Comment in

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