According to a study conducted in China, breast cancer patients with the highest soy consumption had a lower risk of breast cancer recurrence and a lower risk of death than patients with the lowest soy consumption. An editorial that accompanied the study, however, offered some words of caution about these findings. The study and editorial were published in the Journal of the American Medical Association.
Estrogen is thought to play an important role in the development of many breast cancers. Treatments that block the effects of estrogen or inhibit the production of estrogen are commonly used in the treatment of breast cancers that contain estrogen receptors.
Soy foods contain phytoestrogens (plant compounds that share some similarities with estrogen). Phytoestrogens have both estrogen-like and antiestrogenic characteristics, raising questions about the effects of dietary phytoestrogens on breast cancer risk and breast cancer treatment outcomes. Some studies have suggested that soy consumption may reduce the risk of getting breast cancer, but there is relatively little information about the effects of soy after a breast cancer diagnosis.
To explore the relationship between post-diagnosis soy consumption and breast cancer outcomes, researchers evaluated information from the Shanghai Breast Cancer Survival Study. The study enrolled more than 5,000 female breast cancer survivors in China.
- Four-year risk of death was 7.4% among women with the highest intake of soy and 10.3% among women with the lowest intake of soy.
- Four-year risk of breast cancer recurrence was 8.0% among women with the highest intake of soy and 11.2% among women with the lowest intake of soy.
Although these results suggest that dietary soy intake may improve breast cancer outcomes, an accompanying editorial offers some words of caution: “Even though the findings by Shu et al suggest that consumption of soy foods among breast cancer patients is probably safe, studies in larger cohorts are required to understand the effects of these foods among diverse clinical subgroups of breast cancer patients and survivors. In the meantime, clinicians can advise their patients with breast cancer that soy foods are safe to eat and that these foods may offer some protective benefit for long-term health.”
 Shu XO, Zheng Y, Cai H et al. Soy food intake and breast cancer survival. JAMA. 2009;302:2437-2443.
 Ballard-Barbash R, Neuhouser ML. Challenges in design and interpretation of observational research on health behaviors and cancer survival. JAMA. 2009;302:2483-2484.