Risk and prognosis of secondary thoracic cancers after radiation therapy for esophageal cancer

Background and AimRadiation therapy (RT) is a crucial modality for the local control of esophageal cancer (EC), but the effect of RT on the development of secondary thoracic malignancies is still unclear. This study aims to identify the association between RT for the treatment of primary EC and subsequent secondary thoracic cancer (STC). MethodsThe primary EC patients were retrieved from the Surveillance, Epidemiology, and End Results (SEER) database. Fine-Gray competing risk regression and standardized incidence ratio (SIR) were used to evaluate the radiotherapy-associated cancer risk. Overall survival (OS) was compared by Kaplan-Meier analysis. ResultsA total of 40 255 EC patients from the SEER database were identified, of which 17 055 patients (42.37%) did not receive radiotherapy (NRT) and 23 200 patients (57.63%) had been treated with RT. After 12 months of latency, 162 patients (0.95%) in the NRT group and 272 patients (1.17%) in the RT group developed STC. The incidences of the RT group were significantly higher than the NRT group. Patients who have primary EC were at an increased risk of developing STC (SIR = 1.79, 95% CI: 1.63-1.96). The SIR of STC was 1.37 (95% CI: 1.16-1.60) in the NRT group and 2.10 (95% CI: 1.87-2.34) in the RT group. The OS of STC patients in the RT group was significantly lower than the NRT group (P = 0.006). ConclusionThe RT for primary EC was associated with higher risks of developing STC than patients unexposed to radiotherapy. The EC patients treated with RT, especially young patients, require long-term monitoring of the risk of STC.