Role of thoracic radiotherapy for extensive-stage small cell lung cancer in the era of immunotherapy: a review of current evidence.

Extensive-stage small cell lung cancer (ES-SCLC) is an aggressive malignancy with an extremely poor prognosis. For a long time, platinum-based chemotherapy combined with etoposide has been the primary treatment option. Although the initial response rate is high, the vast majority of patients face the dilemma of rapid recurrence and drug resistance. In recent years, the application of immunotherapy has brought about a significant breakthrough in the treatment of ES-SCLC. Multiple Phase III clinical trials have demonstrated that combining immune checkpoint inhibitors with traditional chemotherapy regimens as first-line treatment significantly improves the median overall survival (OS) and progression-free survival (PFS) in patients, while maintaining manageable safety profiles. Therefore, chemotherapy combined with immunotherapy has become the new standard for first-line treatment of ES-SCLC worldwide. However, the absolute survival benefit from immunotherapy remains limited. Against this backdrop, thoracic radiotherapy (TRT), as an effective local treatment modality, shows potential for further survival gains. The combination of chemoimmunotherapy and TRT is emerging as a key area of current clinical exploration. However, the characteristics of the patient population that may benefit most from this treatment modality, as well as the optimal dose and timing of TRT, remain under investigation. Furthermore, the predictive value of previously discussed biomarkers in this combination therapy strategy for ES-SCLC remains unclear. Therefore, this paper reviewed recent advances in treatment strategies and candidate biomarkers for ES-SCLC, with a particular focus on the evolving role of thoracic radiotherapy in the era of immunotherapy.