Scientific review of tamoxifen. Overview from a medical oncologist.

Tamoxifen is a widely used, effective, and well-tolerated agent in the treatment of primary and recurrent breast cancer. In the adjuvant setting, tamoxifen decreases the annual odds of recurrence and death by 25% and 16%, respectively. The toxicities of tamoxifen are of minor concern in the poor-prognosis group of women with metastatic breast cancer. In the more favorable group of women with early breast cancer, the benefits of tamoxifen appear to substantially outweigh the known toxicities. In retrospective analysis, tamoxifen has been consistently demonstrated to decrease the occurrence of contralateral second breast cancer and to be associated with an increased frequency of diagnosis of endometrial carcinoma. It is not known whether tamoxifen is promoting the growth of pre-existing, clinically occult endometrial carcinomas or is truly etiologic for the development of new cancers. The endometrial carcinomas that are associated with tamoxifen appear to have a biology and natural history similar to non-tamoxifen-associated endometrial carcinomas. There is no evidence supporting an association between hepatocellular carcinomas and tamoxifen in humans. Retrospective analysis of the association of colorectal carcinoma and gastric carcinoma provides little convincing evidence of a causal relationship, although further study is warranted.