Consolidation Radiotherapy for Patients with Extended Disease Small Cell Lung Cancer in a Single Tertiary Institution: Impact of Dose and Perspectives in the Era of Immunotherapy

BACKGROUND: Consolidation radiotherapy (cRT) in extended disease small cell lung cancer (ED-SCLC) showed improved 2-year overall survival in patients who responded to chemotherapy (ChT) in CREST trial, however results of two meta - analysis were contradictive. Recently, immunotherapy was introduced to the treatment of ED-SCLC, making the role of cRT even more unclear. The aim of our study was to access if consolidation thoracic irradiation improves survival of ED-SCLC patients treated in a routine clinical practice and to study the impact of cRT dose on survival. We also discuss the future role of cRT in the era of immunotherapy. PATIENTS AND METHODS: We retrospectively reviewed 704 consecutive medical records of patients with small cell lung cancer treated at the Institute of Oncology Ljubljana from January 2010 to December 2014 with median follow up of 65 months. We analyzed median overall survival (mOS) of patients with ED-SCLC treated with ChT only and those treated with ChT and cRT. We also compared mOS of patients treated with different consolidation doses and performed univariate and multivariate analysis of prognostic factors. RESULTS: Out of 412 patients with ED-SCLC, ChT with cRT was delivered to 74 patients and ChT only to 113 patients. Patients with cRT had significantly longer mOS compared to patients with ChT only, 11.1 months (CI 10.1–12.0) vs. 7.6 months (CI 6.9–8.5, p < 0.001) and longer 1-year OS (44% vs. 23%, p = 0.0025), while the difference in 2-year OS was not significantly different (10% vs. 5%, p = 0.19). The cRT dose was not uniform. Higher dose with 45 Gy (in 18 fractions) resulted in better mOS compared to lower doses 30–36 Gy (in 10–12 fractions), 17.2 months vs. 10.3 months (p = 0.03) and statistically significant difference was also seen for 1-year OS (68% vs. 30%, p = 0.01) but non significant for 2-year OS (18% vs. 5%, p = 0.11). CONCLUSIONS: Consolidation RT improved mOS and 1-year OS in ED-SCLC as compared to ChT alone. Higher dose of cRT resulted in better mOS and 1-year OS compared to lower dose. Consolidation RT, higher number of ChT cycles and prophylactic cranial irradiation (PCI) were independent prognostic factors for better survival in our analysis. For patients who received cRT, only higher doses and PCI had impact on survival regardless of number of ChT cycles received. Role of cRT in the era of immunotherapy is unknown and should be exploited in further trials.