Factors associated with survival in small cell lung cancer: an analysis of real-world national audit, chemotherapy and radiotherapy data

BACKGROUND: The mainstay of treatment for small cell lung cancer (SCLC) involves platinum doublet chemotherapy but the optimal duration, 4 vs. 6 cycles, is not known. Concurrent thoracic radiotherapy followed by prophylactic cranial irradiation (PCI) is recommended for fit individuals with limited stage. However, outside of clinical trials, the efficacy of sequential thoracic radiotherapy and PCI for extensive stage is uncertain. METHODS: This retrospective, observational, cohort study used English national lung cancer data to determine the factors associated with survival for all people diagnosed with SCLC. More precisely, for individuals who received chemotherapy, we examined survival by the chemotherapy duration, thoracic radiotherapy dose and the use of PCI. RESULTS: In total 6,438 people were diagnosed with SCLC. We identified that male sex (OR 0.7; 95% CI: 0.62-0.80), increasing age (P=0.01) greater comorbidity (P≤0.01), extensive stage (OR 0.21; 95% CI: 0.19-0.25) and worse performance status (PS2 vs. PS0 adjusted OR 0.38 95% CI: 0.31-0.48) were associated with reduced 1-year survival. Receipt of chemotherapy augmented survival. We analysed data for 1,761 people who had received chemotherapy. Thoracic radiotherapy (≥30 Gy for extensive stage and ≥40 Gy for limited stage) and PCI were independently associated with better survival (P≤0.01 for each), but 6 cycles of chemotherapy instead of 4 was not (limited stage adjusted OR 0.97; 95% CI: 0.48-1.97) extensive stage adjusted OR 1.34; 95% CI: 0.81-2.21). CONCLUSIONS: Extending chemotherapy beyond 4 cycles to 6 does not augment survival. Appropriately prescribed thoracic radiotherapy and PCI can prolong survival in both limited and extensive stage SCLC.