Soy Lowers Risk of Breast Cancer Recurrence

NASHVILLE, Tenn.Although there is a concern regarding the safety of soy-food consumption among breast cancer survivors, researchers found women in China who had breast cancer and a higher intake of soy food had an associated lower risk of death and breast cancer recurrence, according to a study in the December 9 issue of JAMA (2009;302(22):2483-2484).

Soy foods are rich in isoflavones, a major group of phytoestrogens that have been hypothesized to reduce the risk of breast cancer, according to the authors. 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.

Xiao Ou Shu, M.D., Ph.D., of Vanderbilt University Medical Center, Nashville, Tenn., and colleagues examined the association between soy isoflavone intake with breast cancer recurrence and survival. The researchers analyzed data from the Shanghai Breast Cancer Survival Study, a large, population-based study of 5,042 female breast cancer survivors in China. Women ages 20 to 75 years with diagnoses of breast cancer 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 six months after cancer diagnosis and was reassessed at three follow-up interviews conducted at 18, 36 and 60 months after diagnosis. A Shanghai Vital Statistics Registry database was used to obtain survival information for participants who were lost to follow-up.

After a median (midpoint) follow-up of 3.9 years, 444 total deaths and 534 recurrences or breast cancer-related deaths were documented among the group of 5,033 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. Patients in the group with the highest intake of soy protein had a 29- percent lower risk of death during the study period, and a 32-percent lower risk of breast cancer recurrence compared to patients with the lowest intake of soy protein. The adjusted four-year mortality rates were 10.3 percent and 7.4 percent and the four-year recurrence rates were 11.2 percent and 8.0 percent, respectively, for women with the lowest and highest groups of soy protein intake.