The ExCel Trial

The study, referred to as the ExCel trial, is running tests on Aromasin (exemestane), one of a class of new drugs called aromatase inhibitors that block formation of estrogen, which can spur the growth of breast cancer cells.

Such drugs have been found to reduce the relapse rate for breast cancer at least as effectively as tamoxifen, the only other estrogen-blocking drug available. (However, tamoxifen has been found to raise the risk of blood clots, uterine cancer and endometrial cancer, hindering many women from taking it.)

http://www.mercola.com/2005/jun/7/breast_cancer.htm