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Drugs that stimulate ovulation raise endogenous estrogen levels; therefore, concerns persist that such drugs might increase risk for developing breast cancer. As previous studies have yielded mixed results, have included relatively small numbers of patients, and have been of relatively short duration, investigators sought to verify long-term effects by evaluating nearly 10,000 women seen at five U.S. clinics between 1965 and 1988. Just under half received clomiphene citrate, gonadotropins, or both as treatment for infertility. At follow-up, breast cancer rates of users and nonusers were compared, adjusting for confounding factors such as family history of breast cancer, parity, and body-mass index.
Mean age at first evaluation for infertilit…