Endocrine Abstracts

Background: Gender disparity and age pattern in the incidence of thyroid cancer indicate a link between hormonal- and reproductive factors and risk of thyroid cancer. Thus, polycystic ovary syndrome (PCOS) may be a plausible risk factor for this malignancy.

Aim: In this nationwide cohort study, we investigated the association between PCOS and the risk of differentiated and papillary thyroid cancer.

Methods: We included all Danish women born during 1962–1996 (n=990 990). PCOS- and cancer diagnoses, covariates, migration, and vital status were obtained from following Danish, nationwide health- and population registers: The Danish Civil Registration System, the Danish Cancer Register, the Danish National Patient Register, The Danish National Prescription Register, the Danish Medical Birth register, and educational registers at Statistics Denmark. We used the unique, personal identification number assigned to all Danish citizens at birth or immigration, which is used as key identifier all over in the Danish society to link individual level data from the above-mentioned registers. Cox-proportional hazard models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CI) for differentiated thyroid cancer overall and separately for papillary thyroid cancer according to diagnosis of and time since diagnosis of PCOS.

Results: The study cohort comprised 990 850 women. At baseline, 5584 women were diagnosed with PCOS (0.6%). At baseline, Obesity, diabetes type II, use of hormonal contraception, and previous diagnosis of benign thyroid disease were more frequent in women with PCOS, than in women without PCOS. Highest obtained level of education and parity status were similar between the two groups. During follow-up (16 975 570.8 years), we identified 980 women with differentiated thyroid cancer, fifteen of whom were previously diagnosed with PCOS. We found a tendency towards an increased rate of differentiated thyroid cancer in women with PCOS (HR=1.52, 95% CI: 0.91–2.53). The association was strongest in the first 10 years after the PCOS diagnosis (HR=3.81, 95% CI: 1.90–7.65). None of the women were diagnosed with differentiated thyroid cancer within the first three years following PCOS. Results were similar for papillary thyroid cancer.

Conclusions: We found a tendency towards an increased rate of differentiated and papillary thyroid cancer in women with PCOS, which was strongest the first 10 years after PCOS and potentially related to prior benign thyroid disease. Even this large study was limited by few exposed cases and therefore a relatively low statistical power.