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
Five U.S. reproductive endocrinology practices.
Patients
Among a cohort of 12,193 women evaluated for infertility between 1965 and 1988, 9,892 women (81.1% of the eligible population) were followed through 2010 via passive and active (questionnaires) approaches.
Intervention(s)
None
Main Outcome Measure(s)
Hazard ratios (HR) and 95% confidence intervals (CI) for different fertility treatment parameters for select cancers.
Results
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, used by 38.1% of patients, was not associated with colorectal or lung cancer risks, but was related significantly to melanoma and non-significantly to thyroid cancer risks (respective HRs and 95% CIs of 1.95, 1.18–3.22 and 1.57, 0.89–2.75). The highest melanoma risks were seen among those with the lowest drug exposures, but thyroid cancer risk was most enhanced among the heavily exposed patients (HR=1.96, 0.92–4.17 for those receiving >2250 mg.). Clomiphene-associated risks for thyroid cancer were somewhat higher among nulligravid than 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 the assessed cancers.
Conclusions
Our results provide support for continued monitoring of risks of both melanoma and thyroid cancer risk among patients receiving fertility drugs.