Abstract
Soy foods are the major source of isoflavones, which are believed to play important roles in genesis of breast cancer and its progression. We here conducted a prospective study to evaluate the association of soy isoflavone food consumption with breast cancer prognosis. A prospective study was performed from January 2004 and January 2006 in China. Trained interviewers conducted face-to-face interviews using a structured questionnaire to collect information on dietary habits and potential confounding factors. The relative risk [hazard ratio (HR)] and 95% CI were calculated from the Cox regression model for all significant predictors from cancer diagnosis to the endpoint of the study (event). After a median follow up of 52.1 months (range, 9-60 months), a total of 79 breast cancer related deaths were recorded in our study, risk being inversely associated with a high intake of soy isoflavone. With an average intake of soy isoflavone above 17.3 mg/day, the mortality of breast cancer can be reduced by about 38-36%. We also found the decreased breast cancer death with high soy protein intake, with a HR (95% CI) of 0.71 (0.52-0.98). Stratified analysis with reference to the ER status, further demonstrated a better prognosis of ER positive breast cancer with a high intake of soy isoflavone (HR 0.59, 0.40-0.93). Our study shows the soy food intake is associated with longer survival and low recurrence among breast cancer patients. A cohort study with a larger sample size and long term follow-up is now needed.
Highlights
About 1.38 million new cases of breast cancer among women were estimated to have occurred in 2008, making it currently the second most common malignant among women worldwide (10.9% of all cancers)
After a median follow up of 52.1 months, a total of 79 breast cancer related deaths were recorded in our study, risk being inversely associated with a high intake of soy isoflavone
Tamoxifen use, positive estrogen receptor status and receiving chemotherapy were positively associated with the longer survival rate, while smoking and higher TNM stage were inversely related to the poor prognosis (Table 1)
Summary
About 1.38 million new cases of breast cancer among women were estimated to have occurred in 2008, making it currently the second most common malignant among women worldwide (10.9% of all cancers). Most of cases occur both in developed and developing regions with around 690,000 new cases estimated in each region, and the incidence rates vary from 19.3 per 100,000 women in Eastern Africa to 89.7 per 100,000 women in Western Europe (IARC, 2008). Soy foods are the major source of isoflavones, a group of phytoestrogens shows both antiestrogenic and estrogen-like properties. These phytochemicals have been shown to complete with endogenous oestrogens for oestrogen receptors in many in vitro and in vivo systems (Adlercreutz and Mazur, 1997). Breast cancer treatments often lead to a decrease in the endogenous estrogen supply of survivors, and a concern has been raised as to whether soy isoflavones may exert their estrogenic effects, promote cancer recurrence, and negatively influence overall survival (Helferich et al, 2008; Velentzis et al, 2008)
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