Use of Exogenous Hormones and Risk of Papillary Thyroid Cancer (Washington, United States)

Objectives: Greater incidence of thyroid cancer in women than men, particularly evident during the reproductive years, has led to the suggestion that female hormones may increase risk of this disease. We conducted a population-based case-control study in women aged 18 to 64 years in three counties of western Washington State (United States) to assess the relation of use of exogenous hormones, including oral contraceptives (OC) and hormone replacement therapy (HRT), to risk of papillary thyroid cancer.Methods: Of 558 women with thyroid cancer of the follicular epithelium diagnosed during 1988-94 who were identified as eligible, 468 (83.9 percent) were interviewed; this analysis was restricted to women with papillary histology (n = 410). Controls (n = 574) were identified by random digit dialing, with a response proportion of 73.6 percent. Logistic regression was used to calculate odds ratios (OR) and associated 95 percent confidence intervals (CI) estimating the relative risk of papillary thyroid cancer among users of exogenous hormones.Results: Among women aged 45 to 64 years, we observed no association of use of OCs or HRT with risk of papillary thyroid cancer. Among women less than 45 years of age, risk of papillary thyroid cancer was reduced in women who had ever used OCs (OR = 0.6, CI = 0.4-0.9); beyond the relation with ever-use, there was no further association with specific aspects of exposure such as estrogenic potency, latency, recency, age at first or last use, or use at the reference date.Conclusions: Our data do not support the hypothesis that use of exogenous estrogens increases the risk of female thyroid cancer. Cancer Causes and Control 1998, 9, 341-349