1638P Risk and prognosis of secondary lung cancer after radiation therapy for thoracic malignancies

Abstract

Radiation therapy (RT) is a crucial modality for the local control of thoracic cancer (TC), but the effect of pelvic RT on the development of secondary malignancy is still unclear. The aim of this study was to determine the association between exposure to radiotherapy for the treatment of TC and subsequent secondary lung cancer (SLC). The Surveillance, Epidemiology, and End Results (SEER) database (from 1975 to 2015) was queried for the thoracic cancer. Multiple Cox regression analyses and Fine&Gray competing risk regression were employed to assess the cumulative incidence of SLC. Poisson regression and multiple primary standardized incidence ratios (SIR) were used to evaluate the radiotherapy-associated risk for patients receiving RT. Subgroup analyses of patients stratified by latency time since TC diagnosis, age at TC diagnosis, and calendar year of TC diagnosis stage were also performed. Overall survival and secondary lung cancer -related death were compared among the RT and no radiation therapy (NRT) groups by using Kaplan-Meier analysis and competitive risk analysis. A total of 329,129 observations, 147,847 of whom had been treated with RT, and 6,799 patients developed SLC. Receiving radiotherapy was related to a higher risk of developing SLC for TC patients in multiple Cox regression analyses (adjusted HR, 1.25; 95% CI, 1.19-1.32; P<0.001). The cumulative incidence of developing SLC in TC patients with RT (3.8%) was higher than the cumulative incidence (2.9%) in TC patients with NRT (P=0.012). The results of the dynamic SIR and Poisson regression analysis for SLC revealed that a slightly increased risk of SLC was observed after RT in the late-stage latency and was significantly associated to the variations of age at TC diagnosis. The 10-year OS among SLC patients after RT were comparable to SLC patients after NRT in different site of TC. Radiotherapy for thoracic cancer was associated with higher risks of developing secondary lung cancer compared with patients unexposed to radiotherapy.