Ding DC, et al. - In this large, retrospective cohort study, researchers used Taiwan’s National Health Insurance Research Database to investigate if the risk of developing thyroid cancer in Asian women was related to infertility and the use of fertility drugs. The infertile group included 13,356 women aged 20 to 49 years who were diagnosed with infertility from 2000 through 2013, as identified from the insurance claims data, and 53,424 women without a history of infertility and were frequency matched by age and year of diagnosis. The infertile group vs the comparison group had 1.9-fold greater incidence of thyroid cancer. At the end of 7 years of follow-up, the infertile group was found to have a higher cancer incidence. A reduced incidence of thyroid cancer was observed among infertile women who had taken the fertility drug clomiphene vs those who were treated without the drug. However, a nearly 6-fold greater cancer incidence was observed in infertile women being treated with clomiphene vs that in fertile women taking the drug.