Effects of fertility drugs on cancers other than breast and gynecologic malignancies.

Abstract OBJECTIVE: To examine the relationship of ovulation-stimulating drugs to risk of cancers other than breast and gynecologic malignancies. DESIGN: Retrospective cohort study, with additional follow-up since initial report. SETTING: Reproductive endocrinology practices. PATIENT(S): Among a cohort of 12,193 women evaluated for infertility between 1965 and 1988, a total of 9,892 women (81.1% of the eligible population) were followed through 2010, via passive and active (questionnaire) approaches. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Hazard ratios (HRs) and 95% confidence intervals (CIs) for various fertility treatment parameters for select cancers. RESULT(S): During 30.0 median years of follow-up (285,332 person-years), 91 colorectal cancers, 84 lung cancers, 55 thyroid cancers, and 70 melanomas were diagnosed among study subjects. Clomiphene citrate (CC), used by 38.1% of patients, was not associated with colorectal or lung cancer risks, but was related significantly to melanoma (HR = 1.95; 95% CI: 1.18-3.22), and non-significantly to thyroid cancer risks (HR = 1.57; 95% CI: 0.89-2.75). The highest melanoma risks were seen among those with the lowest drug exposure levels, but thyroid cancer risk was greatest among the heavily exposed patients (HR = 1.96; 95% CI: 0.92-4.17 for those receiving >2,250 mg). Clomiphene citrate-associated risks for thyroid cancer were somewhat higher among nulligravid, compared with gravid, women, but did not differ according to distinct causes of infertility. Gonadotropins, used by only 9.7% of subjects, were not related to risk of any of the assessed cancers. CONCLUSION(S): Our results provide support for continued monitoring of both melanoma and thyroid cancer risk among patients receiving fertility drugs.