Thyroid cancer after hysterectomy on benign indications: Findings from an observational cohort study in Sweden.

To investigate the association between hysterectomy and thyroid cancer subtypes based on histopathology. They did a nationwide, population-based, cohort study from 1973 to 2009 in Sweden. All women above 18 years of age during the period between January 1, 1973 and December 31, 2009 from the Register of Population (n = 5.704,202) were identified as the study population. Individual case ascertainment of primary thyroid cancer subtypes were restricted to 1993-2009 based on histological pathologic-anatomical-diagnosis from the Cancer Register. Thyroid cancer subtypes were categorized based on histological morphology as: papillary, follicular and others (including anaplastic and medullary thyroid carcinoma). Information on benign hysterectomy derived from the Swedish Inpatient Register. Women with a hysterectomy (exposed) were compared with women not having had a hysterectomy (unexposed) using Cox's proportional hazard ratios (HRs). The adjusted HR for papillary thyroid cancer was significantly increased in exposed as compared with unexposed women (HR 1.70, 95% CI 1.04-2.79). There was no significant association between hysterectomy and follicular carcinoma or other thyroid cancers. There was a clear shift in the occurrence of thyroid cancer toward a lower attained age at the time of diagnosis among the exposed but no significant difference in overall survival when comparing exposed and unexposed (HR 1.02, 95% CI 0.48-2.16) Hysterectomy was associated with an increased risk for subsequent papillary thyroid cancer and diagnosis at a younger age compared with women not having had a hysterectomy but there were no differences in survival.