The Malaysian Soy and Mammographic Density (MiSo) Study: A Randomized, Three-arm, Controlled Clinical Trial to Investigate the Impact of Soy Isoflavone Intake on Mammographic Density as a Biomarker of Breast Cancer Risk

Globally, breast cancer is the most common cancer and the main cause of deaths due to cancer. This is attributed to changes in reproductive habits as well as an increasingly sedentary lifestyle, with low physical activity and diets rich in saturated fats but low in fiber. While the main focus in many Asian countries is to improve survival from breast cancer by encouraging early detection of the disease and improving access to cancer treatment, it does not reduce the number of women who will be diagnosed with breast cancer in the years to come. Currently, there is an urgent need to develop effective strategies to prevent breast cancer in Asia and beyond.

Soy may be an important dietary strategy for breast cancer prevention. Compared to women in the West, Asian women consume up to 10-fold more soy in their diet, which may, in part, explain their lower risk of breast cancer. Soybeans are rich in isoflavones, which can mimic estrogenic activity. In the body, it competes with estrogen and binds to estrogen receptor sites, thereby reducing the effect of estrogen and possibly lowering breast cancer risk.

Consistently, research has shown that Asian postmenopausal women who have high soy diets are less likely to be diagnosed with breast cancer. However, researchers have not been able to show that postmenopausal women can reduce their breast cancer risk by increasing soy intake as part of their diets. There are several reasons why these studies have failed to see an effect despite the body of evidence indicating that soy may be protective. Firstly, these are studies of Caucasian women who may have never been exposed to soy, particularly in adolescence, where soy may have the greatest impact. Also, these studies have used soy isoflavone supplements, rather than traditional soy foods made from whole soybeans, which may affect how soy is metabolized in the body. Lastly, the way in which mammographic density measurements were obtained previously could have negatively influenced the study results, such as the use of digitized images of mammogram films rather than raw digital images and the use of semi-automated methods that may be subject to human error and reader variability.

Therefore, a well-designed intervention study among Asian women living in Asia, using suitable mammographic density measures as a surrogate marker of breast cancer risk, will best answer these remaining gaps in our knowledge about the soy-breast cancer relationship.