December 8, 2009 — Dietary soy intake among Chinese women with breast cancer is significantly associated with lower risk for death and recurrence, according to the results of a large, population-based cohort study reported in the December 9 issue of the Journal of the American Medical Association.
"Soy foods are rich in isoflavones, a major group of phytoestrogens that have been hypothesized to reduce the risk of breast cancer," write Xiao Ou Shu, MD, PhD, from Vanderbilt University Medical Center in Nashville, Tennessee, and colleagues. "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."
The study goal was to determine the association of dietary soy intake after diagnosis of breast cancer with total mortality and cancer recurrence. In the Shanghai Breast Cancer Survival Study of 5042 female breast cancer survivors in China, women 20 to 75 years of age who were diagnosed between March 2002 and April 2006 were recruited and followed-up through June 2009.
At about 6 months after cancer diagnosis, participants provided information on cancer diagnosis and treatment, lifestyle exposures after cancer diagnosis, and disease progression. Three follow-up interviews at 18, 36, and 60 months after diagnosis allowed updating of this information. To obtain survival information for participants who were lost to follow-up, the investigators used annual record linkage with the Shanghai Vital Statistics Registry database. Disease and treatment information were verified from medical record review.
Primary study endpoints were total mortality and breast cancer recurrence or breast cancer–related deaths. Adjustment for known clinical predictors and other lifestyle factors was performed using Cox regression analysis, with dietary soy intake treated as a time-dependent variable. Median follow-up was 3.9 years (range, 0.5 - 6.2 years).
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