Thyroid cancer risk in women with infertility and association with fertility medications in Taiwan.

ABSTRACT

BACKGROUND: The current study evaluated whether the risk of developing thyroid cancer in Asian women was associated with infertility and the use of fertility drugs. METHODS: The authors conducted a large, retrospective cohort study using Taiwan's National Health Insurance Research Database. From the insurance claims data, a total of 13,356 women aged 20 to 49 years who were diagnosed with infertility from 2000 through 2013 were included in the infertile group, and 53,424 women without a history of infertility were selected as fertile comparisons and were frequency matched by age and year of diagnosis. Both groups were followed up to 2013 to calculate incident thyroid cancer. Poisson regression analysis was used to estimate the incidence rate ratio (IRR). RESULTS: The incidence of thyroid cancer was 1.9-fold greater in the infertile group compared with the comparison group (2.85 vs 1.53 per 10,000 person-years), with an adjusted IRR of 1.80 (95% confidence interval [95% CI], 1.70-1.92) for the infertile group. Higher cancer incidence was demonstrated for the infertile group after 7 years of follow-up, with an adjusted IRR of 4.39 (95% CI, 4.03-4.78) compared with the comparison group. Among infertile women, those who had taken the fertility drug clomiphene were found to have a reduced incidence of thyroid cancer compared with those who were treated without the drug (2.69 vs 3.42 per 10,000 person-years), with an adjusted IRR of 0.86 (95% CI, 0.75-0.99). However, the cancer incidence in infertile women being treated with clomiphene was nearly 6-fold greater than that in fertile women taking the drug. CONCLUSIONS: The results of the current study provide evidence that women with infertility are at an increased risk of developing thyroid cancer.