New Clinical Trial: The Soy Tamoxifen Pevention Trial
by Laura J. Esserman, M.D., M.B.A

Measuring the long-term impact of specific drugs on the development of breast cancer can take years or even decades and cost millions of dollars. In this study, we are instead going to look at markers of risk to see whether drugs like tamoxifen or natural substances like soy can affect these markers.

What is a biologic marker of risk? It is different from risk factors. Risk factors refer to characteristics that are more common in women who have a particular disease. In the case of breast cancer, known risk factors include a family history of cancer, a history of alcoholism, early age of menarche (time of starting menstruation), late menopause, no children or late child bearing. However, about half of the women who get breast cancer do not have any of these risk factors. Furthermore, risk factors are often conditions that cannot be influenced, so they do not help us to design prevention studies.

Biologic markers, on the other hand, can often be changed. They can be measured, and we are just beginning to understand which ones are meaningful for predicting breast cancer risk. One marker that has emerged is breast density. This can be measured by mammography as well as by other studies. It is something that can be changed. Another marker that looks very promising is the finding of atypical or abnormal cells from some kind of breast biopsy or from ductal lavage (getting fluid from the milk ducts). Yet another marker may be the serum hormone levels. These may be important not only in predicting who is at higher risk for breast cancer but who is likely to benefit from therapies such as tamoxifen.

Our Soy-Tamoxifen Trial is designed to see whether soy or tamoxifen, when taken for 6 months, can cahange breast density or the types of cells that are found in the breast ducts. We are also going to draw blood to measure serum hormone levels to hopefully help us to figure out whether some women benefit more than others from soy or tamoxifen.

This first study is for premenopausal women with dense breasts who are at higher risk for developing breast cancer. Women who participate will have a 50% chance of being assigned to soy, a 25% chance of being given tamoxifen, or a 25% chance of being given a placebo. The study will go on for only 6 months, after which participants are free to pursue whatever therapy they choose.

There is a great need to get more information on how soy works. Many people assume that it prevents breast cancer, but this is not yet proven. Please call our Prevention Program at (415)353-7029 for more information or if you would like to participate in one of our prevention studies.