Chemoprevention of Breast Cancer Hormonal manipulation is being tested in the primary prevention of breast cancer. Tamoxifen is an antiestrogen with partial estrogen agonistic activity in some tissues, such as endometrium and bone. One of its actions is to upregulate transforming growth factor β, which decreases breast cell proliferation. In randomized placebo-controlled trials to assess tamoxifen as adjuvant therapy for breast cancer, tamoxifen reduced the number of new breast cancers in the opposite breast by more than a third. In a randomized placebo-controlled prevention trial involving 13,000 women at high risk, tamoxifen decreased the risk of developing breast cancer. | Chapter 078. Prevention and Early Detection of Cancer Part 5 Chemoprevention of Breast Cancer Hormonal manipulation is being tested in the primary prevention of breast cancer. Tamoxifen is an antiestrogen with partial estrogen agonistic activity in some tissues such as endometrium and bone. One of its actions is to upregulate transforming growth factor ß which decreases breast cell proliferation. In randomized placebo-controlled trials to assess tamoxifen as adjuvant therapy for breast cancer tamoxifen reduced the number of new breast cancers in the opposite breast by more than a third. In a randomized placebo-controlled prevention trial involving 13 000 women at high risk tamoxifen decreased the risk of developing breast cancer by 49 from to per 1000 women after a median followup of nearly 6 years. The International Breast Cancer Intervention Study IBIS-I trial had similar findings. In both studies tamoxifen also reduced bone fractures a small increase in risk of endometrial cancer stroke pulmonary emboli and deep vein thrombosis was noted. Tamoxifen has been approved by the . Food and Drug Administration for reduction of breast cancer in women at high risk for the disease risk at 5 years based on the Gail risk model http cancertopics pdq genetics breast-and-ovarian healthprofessional Section 66 . A trial comparing tamoxifen with another selective estrogen receptor modulator raloxifene showed that raloxifene is comparable to tamoxifen in cancer prevention. Raloxifene is associated with more noninvasive breast cancer than tamoxifen the drugs are similar in risks of other cancers fractures ischemic heart disease and stroke. Because the aromatase inhibitors are even more effective than tamoxifen in adjuvant breast cancer therapy it is hoped that they also are more effective in breast cancer prevention. However no data are available on this point. Chemoprevention of Prostate Cancer Finasteride is a 5-a-reductase inhibitor. It inhibits
