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.