Impact of radiotherapy on second primary lung cancer incidence and survival in esophageal cancer survivors

Esophageal cancer, ranked as the seventh most common cancer globally, encompasses squamous cell carcinoma and adenocarcinoma. Despite advancements in treatment modalities like surgery, chemotherapy, radiotherapy, and immunotherapy, radiotherapy, while crucial for enhancing local control and survival, poses risks for long-term side effects and the development of second primary malignancies (SPM), notably Second primary lung cancer (SPLC). This study aims to analyze the incidence of second primary lung cancer (SPLC) among esophageal cancer survivors, with a focus on the influence of radiotherapy, analyze variations across different demographic and clinical subgroups, and assess patient survival outcomes. Using data from the Surveillance, epidemiology, and end results (SEER) program on 56,493 esophageal cancer patients (2000-2020), we compared SPLC incidence in those with and without prior radiotherapy. We applied a competing risks framework, propensity score matching (PSM), and survival analyses to assess SPLC risk and radiotherapy's impact. The study showed that patients treated with radiotherapy have a significantly higher long-term risk of SPLC compared to those without it. Radiotherapy significantly raised SPLC risk (HR 1.41, 95% CI 1.06-1.88), with higher SIRs particularly in younger patients and females. Post-PSM, there were significant differences in cancer-specific survival between esophageal cancer survivors with post-radiotherapy SPLC and those with only primary lung cancer. This cohort study shows that radiotherapy in esophageal cancer survivors increases SPLC risk but does not worsen survival compared to those with OPLC, highlighting the need for long-term monitoring and management.