Survival Outcomes for Oligometastatic vs. Polymetastatic Extensive-Stage Small Cell Lung Cancer Following Consolidative Thoracic Radiotherapy

Abstract

For patients with limited metastatic burden, metastasis-directed radiotherapy has been shown to be associated with improved OS for certain types of cancer. However, these prior trials did not include patients with ES-SCLC. It is not yet clear if patients with oligometastatic ES-SCLC have improved outcomes over polymetastatic ES-SCLC after cTRT. We identified patients treated with cTRT for ES-SCLC in 2013-2020 at a single institution. Oligometastatic disease was defined at the time of diagnosis as three or fewer organs with distant disease, and with each organ having three or fewer metastatic lesions. All other patients were considered polymetastatic. The Kaplan-Meier estimator, log-rank test, and multivariable Cox proportional hazards regression were used to compare OS, progression-free survival (PFS), local recurrence-free survival (LRFS), and new metastasis-free survival (NMFS) between oligometastatic and polymetastatic ES-SCLC patients undergoing cTRT. Among 70 included patients, 36 were defined as oligometastatic. All patients received platinum-doublet chemotherapy and cT. Immunotherapy was given in 7 (19.4%) oligometastatic patients and 5 (14.7%) polymetastatic patients (p = 0.56). Median follow-up time was 38.2 months. Multivariable Cox regression analysis showed that oligometastatic disease (vs. polymetastatic disease) at diagnosis was associated with improved OS (hazard ratio [HR] 0.44, 95% CI 0.25-0.78, p = 0.005, 1-year OS 86.1% vs. 46.9%, 2-year OS 47.1% vs. 15.1%). PFS, LRFS, and NMFS were not significantly different between the cohorts. Among oligometastatic patients, pleural involvement (HR 2.44, 95% CI 1.02-5.83, p = 0.046) and lung involvement (HR 4.93, 95% CI 1.02-23.9, p = 0.047) were associated with inferior OS. Among the 26 of 36 (72.2%) oligometastatic patients with neither pleural nor bilateral lung involvement, 1-year OS was 88.5% and 2-year OS was 58.3%. We observed that oligometastatic ES-SCLC patients treated with cTRT (especially those without pleural or bilateral lung involvement) have superior OS than those with polymetastatic disease. We encourage enrollment on the NRG LU007/RAPTOR randomized trial to determine the impact of complete or incomplete consolidative RT to up to 5 sites in ES-SCLC, especially in those with oligometastatic disease.