Increased risk of papillary thyroid cancer related to hormonal factors in women.

Strikingly higher rates of papillary thyroid cancer in women compared with men suggest that hormonal factors may be involved in the development of this cancer. A number of independent studies have investigated the association between hormonal factors and papillary thyroid cancer risk in women but yielded conflicting and inconclusive findings. We performed a meta-analysis of all currently published studies to provide better estimates for the risk of papillary thyroid cancer related to menstrual, reproductive, and other hormonal factors in women. Six cohort studies and three case-control ones were included into our study after a comprehensive literature search. The pooled relative risk (RR) with 95 % confidence interval (95 % CI) implicated that late age at menopause was associated with an increased risk of papillary thyroid cancer (RR = 1.39, 95 % CI 1.03-1.89, P = 0.032). No significant association was demonstrated between papillary thyroid cancer risk and other hormone-related factors, including oral contraceptive, hormone replacement therapy, age at menarche, parity, age at first birth, menopausal status, and breast feeding. Subgroup analysis by study design confirmed those associations. Sensitivity analysis did not materially alter the pooled results. The meta-analysis firstly suggests that late age at menopause is a risk factor for papillary thyroid cancer.