Impact of thoracic radiation therapy after chemotherapy on survival in extensive‐stage small cell lung cancer: A propensity score‐matched analysis

BACKGROUND: The role of thoracic radiation therapy (TRT) after chemotherapy (CHT) in extensive‐stage small cell lung cancer (ES‐SCLC) has not been well defined. We investigated whether intensity‐modulated radiotherapy (IMRT) improves outcomes in ES‐SCLC after CHT compared to CHT alone. METHODS: A total of 292 patients who reached a complete response (CR), partial response (PR), or stable disease (SD) after CHT were assigned into groups: CHT + TRT and CHT alone. Propensity score matching was used to balance patient groups (n = 72 each). RESULTS: The five‐year overall survival (OS: 12.3% vs. 3.6%; P < 0.001) and progression‐free survival (PFS: 3.2% vs. 1.7%; P = 0.006) rates were significantly higher in the CHT + TRT group. This data was confirmed in the matched samples (5‐year OS: 10.5% vs. 1.6%, P < 0.001; PFS: 4.3% vs. 0.0%, P = 0.023). The overall (P = 0.002) and locoregional (P < 0.001) recurrence rates in the CHT + TRT group were significantly lower than in the CHT group. Univariate analysis showed that response evaluation after CHT and TRT were significant prognostic factors of OS. Multivariate analyses revealed that N Stage 0–1 (P = 0.02), > 6 cycles of CHT (P = 0.042), CR + PR after CHT (P < 0.001), and TRT (P < 0.001) were independently associated with longer OS compared to CHT alone. CONCLUSION: TRT using IMRT is strongly correlated with improved OS and PFS in ES‐SCLC patients reaching CR, PR or SD after CHT. A multicenter, randomized phase III clinical trial is needed to confirm these findings.