Tran TVT, Maringe C, Majano SB, et al. - Researchers investigated whether thyroid dysfunction was related to risk of breast cancer among 239,436 females of the UK Biobank cohort. Using baseline self-reported data and hospital inpatient databases, data regarding thyroid dysfunction, personal and family medical history, medications, reproductive factors, lifestyle, and socioeconomic characteristics were obtained. Using population-based registries, breast cancer diagnoses were found. The study sample comprised 3,227 (1.3%) and 20,762 (8.7%) females with hyper- and hypothyroidism prior to the baseline. A median follow-up of 7.1 years revealed breast cancer development in 5,326 (2.2%) women. Findings showed a decreased risk of breast cancer long after hypothyroidism diagnosis, but an elevated risk was evident in females with treated hyperthyroidism.