Immunotherapy Improves Survival and Reduces Brain Metastasis Risk in Limited- Stage Small Cell Lung Cancer Patients Receiving Prophylactic Cranial Irradiation

Background This study aimed to evaluate the impact of immunotherapy on survival and brain metastasis (BM) risk in patients with limited-stage small cell lung cancer (LS-SCLC) undergoing prophylactic cranial irradiation (PCI), and to analyze related prognostic factors. Methods A retrospective analysis was conducted on 103 LS-SCLC patients who received PCI between February 2016 and July 2024. Patients were categorized into immunotherapy (n = 42) and non-immunotherapy (n = 61) groups. The Kaplan-Meier method and Cox proportional hazards models were used for survival and prognostic analysis. Results The median overall survival (mOS) for the entire cohort was 32.0 months (95% CI: 26.8–37.2). The immunotherapy group demonstrated significantly prolonged mOS (38.0 vs. 27.0 months, p = 0.019) and a lower 3-year BM rate (10.8% vs. 31.7%, p = 0.035) compared to the non-immunotherapy group. Subgroup analysis revealed that patients receiving immunotherapy before-PCI (n = 27) had more pronounced OS benefit (mOS: 40.0 vs. 27.0 months, p = 0.007) and lower BM risk (3-year BM rate: 7.7% vs. 31.7%, p = 0.018) than the non-immunotherapy group. Multivariate analysis identified immunotherapy (HR = 0.48, p = 0.008), no smoking history (HR = 0.46, p = 0.004), and the presence of extracranial metastasis (HR = 1.92, p = 0.012) as independent factors for OS. Immunotherapy (HR = 0.25, p = 0.019) and no smoking history (HR = 0.20, p = 0.008) were independent protective factors against BM. Conclusion For LS-SCLC patients receiving PCI, early integration of immunotherapy, particularly before PCI, effectively reduces the incidence of brain metastasis and significantly improves survival. Smoking history remains a significant adverse prognostic factor in clinical management.