Age-related risk for second breast cancer and gynecological malignant neoplasms after differentiated thyroid cancer

In this study, we aimed to investigate the age-related risk of second breast cancer (SBC) and second gynecological malignant neoplasms (SGMNs) in female differentiated thyroid cancer (DTC) survivors by utilizing the Surveillance, Epidemiology, and End Results (SEER) database.A total number of 55,622 female DTC patients were identified between 1975 and 2016, including 2168 patients who developed SBC and SGMNs. The Fine and Gray model was used to calculate the cumulative incidence and sub-distribution hazards ratios (SHR). Poisson regression analysis was employed to calculate the relative risk (RR) and standardized incidence ratio (SIR). Kaplan-Meier survival and log-rank test analyses were also performed.The overall 40-year cumulative incidence of SBC and SGMNs was 18.9%. Their incidence in the adolescent and young adults (AYA) group increased slowly in the first 30 years, but then was rapidly elevated in the last decade. It increased gradually in the middle-aged adults group and in the first 25 years in the older adults group, but it scarcely increased thereafter. Both the middle-aged adults (adjusted SHR, 2.09; RR, 1.76) and the older adults (adjusted SHR, 1.32; RR, 1.58) groups had higher risks of developing combined SBC and SGMNs than the AYA group. The risks increased mainly in the early latency period. The three groups also had higher SIRs than the US general population. Besides, the best survival after SBC and SGMNs was observed in the AYA group.Age was an independent risk factor for SBC and SGMNs incidences among female DTC survivors.