Infertility drugs and the risk of breast cancer: findings from the National Institute of Child Health and Human Development Women's Contraceptive and Reproductive Experiences Study.

OBJECTIVE: To determine the association between infertility drug use and invasive breast cancer in a population-based case-control study.
DESIGN: Multicenter case-control study.
SETTING: Women aged 35 to 64 years in metropolitan Atlanta, Detroit, Los Angeles, Philadelphia, and Seattle. PATIENT(S): The 4,575 case patients had histologically confirmed primary invasive breast cancer. The 4,682 control subjects were women without breast cancer identified in the same geographic locations using randomized-digit dialing. INTERVENTION(S): A standardized questionnaire focusing on reproductive health and family history as well as use of oral contraceptives and other hormones and infertility drugs was administered to all subjects. Data on the type of breast cancer were also obtained. MAIN OUTCOME MEASURE(S): Odds ratios examining the association between use of various infertility drugs and invasive breast cancer. RESULT(S): Overall, a history of infertility drug use was not associated with the risk of developing breast cancer. Compared with women who never used any fertility medication, however, women using human menopausal gonadotropin (hMG) for > or = 6 months or for at least six cycles had a relative risk of breast cancer ranging between 2.7 to 3.8. CONCLUSION(S): Long-term use of certain infertility drugs could adversely affect risk of breast cancer. Additional confirmatory studies are needed.