Increased estrogen and the risk of papillary thyroid cancer

Objectives/Hypothesis: Papillary thyroid carcinoma (PTC) is more common in women with a female:male incidence ratio of 3:1. Estrogen has been implicated in the development of thyroid cancer. The study investigates the relationship between various estrogenassociated risk factors, including benign and malignant uterine and breast disease and pregnancy, in a large group of women with thyroid disease. Study Design: Retrospective chart review of all patients with thyroid disease at a single tertiary care center over a 12 year period. Methods: 787 female patients diagnosed with thyroid disease between 1997-2009 were included. Charts were reviewed and patients were segregated into benign or malignant disease. Odds ratios were calculated for the following risk factors: history of hysterectomy, uterine fibroids, breast adenoma, and pregnancy. Statistical analyses were performed using the Fisher's exact test. Results: 259 patients had a history of papillary thyroid carcinoma. 50% of the PTC patients had a history of pregnancy compared to 41.7% of the patients with benign thyroid disease. The odds ratio associated with pregnancy was 1.43 (95% CI 1.00 - 1.89, p = 0.024). Overall, PTC patients were 43% more likely to have a history of pregnancy than those with benign disease. Odds Ratios were calculated for all risk factors and subsets of malignancy, but none demonstrated statistical significance. Conclusion: A history of pregnancy, a hyperestrogenic state, is associated with an increased risk of papillary thyroid carcinoma. This further supports the role of estrogen in the pathogenesis of thyroid cancer.