A new study performed on Aromasin, an anti-estrogen drug, found the drug capable of cutting the odds of breast cancer in high-risk postmenopausal women by 65%. Unlike other anti-estrogen therapies such as tamoxifen and raloxifene, Aromasin (exmestane) did not carry an increased risk of endocrine cancer or blood clots, though it did have the common problems of hot flashes and joint stiffness also experienced with tamoxifen and raloxifene. Estrogen is a primary factor behind many breast cancers.
Aromasin, an aromatase inhibitor manufactured by Pfizer – who partially funded the study, is currently approved for early breast cancer patients but not to prevent tumors. This new study is considered the first to look at the drug’s use for prevention.
Tamoxifen and its sister drug, raloxifene, which are selective estrogen receptor modulators (SERMs), are approved for breast cancer prevention in high-risk women but both have serious, if rare, side effects, including endometrial cancer and blood clots.
Tamoxifen has been shown to reduce the risk of invasive breast cancer by 38%, but the risk of side effects seems to have discouraged many women from taking it. Only 4% of women eligible to take tamoxifen actually do so, noted Dr. Paul E. Goss, lead author of the new study and professor of medicine at Harvard Medical School and Massachusetts General Hospital in Boston.
The new phase 3 trial included 4,560 women, all of whom were at higher risk of breast cancer and were randomly selected to take either Aromasin or a placebo. After an average 3-year follow-up, investigators found a 65% reduction in invasive breast cancer in the Aromasin group compared to the placebo group, a difference Dr. Goss characterized as “massive”. The researchers also hoped that osteoporosis and cardiovascular side effects would also be lower in the Aromasin group, but they were not.
However, it was stressed, that the 3-year follow-up period was relatively short, and that patients do need to be followed for longer.