2021 - Role of Thoracic Radiotherapy in Extensive-Stage Small Cell Lung Cancer Patients with Baseline Brain Metastases: A Retrospective Analysis Using IPTW-Adjusted Models

Z. Chaonan¹, W. Wang², L. Deng², N. Bi³, T. Zhang¹, J. Wang⁴, W. Liu Jr¹, Z. Xiao¹, Q. Feng¹, and Z. Zhou¹; ¹Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China, ²Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences (CAMS) and Peking Union Medical College (PUMC), Beijing, China, ³Cancer Hospital Academy of Medical Sciences, Beijing, China, ⁴Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China

Purpose/Objective(s): To investigate the efficacy of thoracic radiotherapy (TRT) in extensive-stage small-cell lung cancer (ES-SCLC) patients with baseline brain metastases. Materials/

Methods: The study cohort consisted of 89 patients diagnosed as ES-SCLC with baseline brain metastases at our hospital between January 2013 and June 2023. Patients were stratified into two groups based on their receipt of TRT. Categorical variables were compared using either the Chi-squared test or Fisher’s exact test. Overall survival (OS) and progression-free survival (PFS) were assessed using the Kaplan-Meier method, and potential imbalances were corrected for using the inverse probability of treatment weighting (IPTW) method. Cox proportional hazards regression models were utilized to estimate the risk factors associated with OS.
Results: 89 ES-SCLC patients with baseline brain metastases were included, with the median age of 63 years (range: 33-77 years). Among these patients, 50 received thoracic radiotherapy (TRT), while 39 did not. A total of 31 patients received immunotherapy, with 28 of them receiving immunotherapy during first-line treatment. Baseline characteristics were well-balanced between the two groups after IPTW adjustment. The median PFS was 8.0 months in the TRT group and 6.0 months in the No-TRT group (p=0.02). OS was significantly longer in the TRT group compared to the No-TRT group based on both unadjusted data (median OS: TRT vs No-TRT, 13 vs 25 months, p < 0.001) and IPTW-adjusted data (median OS: 13 vs 19 months, p < 0.001). In unadjusted multivariate Cox analysis, TRT remained a significant prognostic factor for OS (Hazard Ratio [HR]: 0.35, 95% Confidence Interval [CI]: 0.15-0.79, p = 0.01). Additionally, receipt of immunotherapy was also associated with better prognosis (HR: 0.29, 95% CI: 0.11-0.75, p = 0.01). However, subgroup analyses suggested that TRT did not particularly benefit patients who received immunotherapy (HR: 0.31, 95% CI: 0.05-1.98, p = 0.2). Notably, among the 49 patients who received brain radiotherapy (BRT), TRT was associated with better OS (HR: 0.29, 95% CI: 0.13-0.62, p = 0.002), which was not observed in patients who did not receive BRT.
Conclusion: TRT provided significant OS benefits in ES-SCLC patients with baseline metastases, particularly in those who received brain radiotherapy.