USE OF EXOGENOUS HORMONES AND RISK OF PAPILLARY THYROID-CANCER (WASHINGTON, UNITED-STATES)

Objectives: Greater incidence of thyroid cancer in women than men, par ticularly evident during the reproductive years, has led to the sugges tion that female hormones may increase risk of this disease. We conduc ted a population-based case-control study in women aged 18 to 64 years in three counties of western Washington State (United States) to asse ss the relation of use of exogenous hormones, including oral contracep tives (OC) and hormone replacement therapy (HRT), to risk of papillary thyroid cancer. Methods: Of 558 women with thyroid cancer of the foll icular epithelium diagnosed during 1988-94 who were identified as elig ible, 468 (83.9 percent) were interviewed; this analysis was restricte d 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 rel ative risk of papillary thyroid cancer among users of exogenous hormon es.Results: Among women aged 45 to 64 years, we observed no associatio n of use of OCs or HRT with risk of papillary thyroid cancer. Among wo men less than 45 years of age, risk of papillary thyroid cancer was re duced 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 spec ific 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.