Tamoxifen is a drug used to treat early stage and metastatic breast cancer. The American Society of Clinical Oncology (ASCO) recommended consideration of tamoxifen therapy for reduction of breast cancer risk in women with projected 5-year risk greater than 1.66 percent. The decision to take tamoxifen should be made carefully because tamoxifen therapy has many serious side effects.
Endometrial Cancer
Tamoxifen use has been linked to increased risk of endometrial cancer. Data based on the National Surgical Adjuvant Breast and Bowel Project P-1 Study (NSABP-P1), the Royal Marsden Hospital trial (RMH) and the International Breast Cancer Intervention Study I (IBIS-1) indicated that tamoxifen therapy increases risk of developing endometrial cancer by 2-to-4 fold. For instance, in the NSABP-P1 trial, the rates of endometrial cancers were 0.8 cancers in 1,000 women taking placebo and 3.1 cancers in 1,000 women taking tamoxifen over a period of 55 months. Studies also showed that tamoxifen also slightly increases the risk of uterine sarcoma, another type of cancer that can develop in the uterus.
Thromboembolism
Tamoxifen increases risk of developing blood clots in the blood vessels and consequently risk of developing various thromboembolic events. According to the results of the Breast Cancer Prevention Trial, tamoxifen was found to increase the risk of having stroke by 75 percent, the risk of developing pulmonary embolism by roughly 200 percent and the risk of deep vein thrombosis by 70 percent. Tamoxifen is found to have no statistically significant impact on risk of having heart attacks. Older women are recommended to consult with their physicians about their risk of developing blood clots when taking tamoxifen.
Cataract
Cataract is the clouding of the lens of the eye. According to the U.S. Preventive Services Task Force (USPSTF), tamoxifen therapy slightly increases the risk of developing cataract by 10 to 15 percent and the risk of having cataract surgery by 50 percent.
Osteoporotic Fracture
Use of tamoxifen prevents bone loss and reduces risk of bone fractures. A review of data from the NSABP-P1, the RMH trial and the IBIS-I indicated that tamoxifen therapy reduces risk of osteoporotic fracture, such as hip fracture, by 15 to 20 percent.
