Abstract B125: Reproductive factors and thyroid cancer risk: The multiethnic cohort study

Background : Thyroid cancer is the most common endocrine cancer worldwide, with the incidence in women being three times that of men. Several reproductive and hormonal factors have been proposed as possible contributors to thyroid cancer risk, including age at menarche, parity, age at menopause, oral contraceptive use, surgical menopause, and hormone replacement therapy. Our study aimed to investigate potential reproductive/hormonal factors in a multiethnic population. Methods : A prospective cohort study of women of diverse racial and ethnic groups in the Multiethnic Cohort Study (n=118,344) was used. Included were 373 papillary thyroid cancer cases, linked to SEER cancer incidence and statewide death certificate files in Hawaii and California. Exposures investigated include age at menarche, parity, menopausal status and type, birth control use, and outcomes of first pregnancy. Cox proportional hazards models of papillary thyroid cancer were used to obtain relative risk (RR) and 95% confidence intervals (CI) to examine the associations with reproductive/hormonal factors. Results : We observed a statistically significant increased risk of papillary thyroid cancer for hysterectomy, oophorectomy, surgical menopause, and not having a child by age 20. The adjusted estimates for oophorectomy RR 1.66 (95% CI: 1.31, 2.11) and hysterectomy RR 1.82 (95% CI: 1.42, 2.34). Menopause due to surgery was associated with a 55% increase in risk (RR 1.55, 95% CI: 1.22, 1.97) and nulliparity vs ≤ 20 years of age at first livebirth was related to a 51% increased risk (adjusted RR 1.51, 95% CI: 1.07, 2.15). Adjustment factors included age and race/ethnicity and menopausal status, menopausal type, and oral contraception where appropriate. Former use of estrogen menopausal hormone therapy was associated with a 35% increased risk (adjusted RR: 1.35, 95% CI: 1.02, 1.79). No significant heterogeneity was seen in these associations by race/ethnicity (p het >0.48). Conclusion : The reproductive risk factors for papillary thyroid cancer reported in the literature were largely confirmed in our multiethnic population. Our analysis finds having a hysterectomy or oophorectomy and the use of MHT are associated with an increased risk of papillary thyroid cancer, and having a child at a younger age is associated with a reduction in thyroid cancer risk. Citation Format: Janine V. Abe, Song-Yi Park, Christopher A. Haiman, Loïc Le Marchand, Brenda Y. Hernandez, Lynne R. Wilkens. Reproductive fa