Study: Why Tamoxifen Fights Cancer in Breast But Not Uterus

Harvard Medical School researchers report that a gene-activating protein may be the factor that explains why the drug tamoxifen fights cancer in the breast but increases the risk of cancer in the uterus.

Drs. Yongfeng Shang and Myles brown, reporting in the journal Science, said the presence of a protein called steroid receptor coactivator 1 (SRC-1) may be key to why tamoxifen effects some tissues differently than others.

Tamoxifen, widely prescribed for women who have breast cancer that is sensitive to the effects of the hormone estrogen, is a selective estrogen receptor modulator (SERM) that "recruits" molecules that repress genes that promote cancer growth in breast cancer cells, but help recruit molecules that promote cancer in uterine cancer cells.

The explanation, the researchers said, may lie in the fact that the SRC-1 protein is more abundant in the uterus than in the breast.

A newer SERM, raloxifene, works the same way as tamoxifen in breast cancer cells, but does not recruit the cancer-promoting molecules in uterine cancer cells.

Drs. Benita S. Katzenellenbogen and John A. Katzenellenbogen of the University of Illinois at Urbana-Champaign, in a related editorial, say the understanding of how these molecules work "provides a foundation for the development of SERMs that are optimized for breast cancer prevention and treatment, and menopausal hormone replacement."

Other Sources: Science