Soy Isoflavone Intake Significantly Reduces Risk of Breast Cancer Recurrence, May Improve Survival
It has been suggested in previous studies that soy isoflavones have anticancer properties; however, it is also known that soy-based foods possess estrogen-like properties and can therefore present complications rather than benefits for patients with breast cancer, potentially even playing a role in the genesis of breast cancer or its progression. Now 2 new studies indicate that daily consumption of soy-based foods may confer benefits for patients with breast cancer.
In the first study, the investigators prospectively evaluated the potential association between consumption of soy-based foods after a diagnosis of breast cancer and cancer outcomes among American and Chinese women (Nechuta SJ, et al. Am J Clin Nutr. 2012;96:123-132).
The data for the analysis came from the After Breast Cancer Pooling Project and included data for 9514 breast cancer survivors from 2 US cohorts and 1 Chinese cohort. All patients had a diagnosis of invasive breast cancer between 1991 and 2006. The findings were adjusted for clinical, sociodemographic, and lifestyle factors.
At a mean follow-up of 7.4 years, 1171 women died, 881 of whom died from breast cancer. In addition, a total of 1348 breast cancer recurrences occurred after that period. Despite large differences in daily intake of soy isoflavone between the Chinese and the American women, soy isoflavone consumption was inversely associated with cancer recurrence in both populations. This was true when the data were analyzed specifically by country, as well as when the data were combined for both populations.
Overall, consumption of ≥10 mg daily of soy isoflavones was associated with a nonsignificant increased reduction of all-cause mortality risk (HR, 0.87; 95% CI, 0.70-1.10), as well as nonsignificant risk reduction of breast cancer–specific mortality (HR, 0.83; 95% CI, 0.64-1.07). However, the risk reduction of disease recurrence was significantly greater with daily consumption of ≥10 mg of soy products (HR, 0.75; 95% CI, 0.61-0.92). These findings indicate that regular consumption of soy products can reduce the risk of recurrence in some women with breast cancer. Further studies are needed to confirm these data, and to elucidate specifically which types of breast cancer can benefit from these products.
The second prospective study was conducted in China and included Chinese women only (Zhang YF, et al. Asian Pac J Cancer Prev. 2012;13:479-482). The study was conducted between January 2004 and January 2006. Data were collected via face-to-face interviews, using questionnaires related to dietary habits and confounding factors.
After a median follow-up of 52.1 months (range, 9-60 months), 79 deaths related to breast cancer were reported. The data indicate that breast cancer–related mortality risk was inversely associated with a high intake of soy products. An average intake of >17.3 mg daily of soy isoflavones was found to be associated with a 36% to 38% mortality risk reduction. Similarly, a high intake of soy protein was associated with a reduction in breast cancer–related death (HR, 0.71; 95% CI, 0.52-0.98).
Furthermore, a stratified analysis of estrogen receptor (ER) status suggested that ER-positive status is still associated with an improved prognosis with high intake of soy isoflavones (HR, 0.59; 95% CI, 0.40-0.93).