Impact of prophylactic cranial irradiation on survival in extensive-stage small cell lung cancer receiving first-line chemoimmunotherapy: a propensity score-matched study.

Background: Chemoimmunotherapy has emerged as the standard first-line treatment for extensive-stage small cell lung cancer (ES-SCLC), improving survival outcomes. However, the role of prophylactic cranial irradiation (PCI) in the context of chemoimmunotherapy remains undefined.

Objectives: This study aimed to evaluate the impact of PCI on overall survival (OS) in patients with ES-SCLC after chemoimmunotherapy administration.

Design: Retrospective study.

Methods: This retrospective analysis included 261 patients with ES-SCLC treated with first-line chemoimmunotherapy between January 2019 and December 2023. All patients underwent MRI scans to confirm the absence of brain metastases. After 1:2 propensity score matching (PSM), 46 and 81 patients were assigned to the PCI and observation groups, respectively. The primary endpoint was OS, with additional exploration of progression-free survival (PFS), the cumulative incidence of intracranial metastases, and intracranial progression-free survival (iPFS).

Results: After PSM, the two groups were well-balanced in baseline characteristics. Survival analysis showed a median OS of 19.9 months (95% confidence interval (CI): 11.8-28.0) in the PCI group and 15.6 months (12.3-18.9) in the observation group, without a significant difference (hazard ratio (HR) = 0.763 (95% CI: 0.484-1.206), log-rank p = 0.265). PCI significantly reduced the risk of brain metastasis (Fine-Gray p = 0.002), with 1-year cumulative incidence rates of 13.8% (3.4%-24.2%) in the PCI group and 53.4% (41.3%-65.6%) in the observation group. Subgroup analysis showed that for ES-SCLC patients achieving a partial response to initial chemoimmunotherapy, the PCI group had longer median OS (25.7 months (95% CI: 15.4-36.1) vs 19.4 months (15.4-23.4); HR = 0.502 (0.284-0.886); log-rank p = 0.021).

Conclusion: PCI did not improve OS in ES-SCLC patients receiving first-line chemoimmunotherapy, while it may confer a survival benefit for patients who achieve remission following chemoimmunotherapy. In addition, PCI significantly reduced the incidence of brain metastases. These findings warrant further randomized studies for verification.