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Outcomes for patients with inoperable locally advanced non-small cell lung cancer (LA-NSCLC) are poor, with a median survival of about 2 years (1) and a 5-year survival of about 10–15% following diagnosis, even among patients with good performance status at presentation (2). Despite these poor outcomes, conventional radiation therapy (RT) with chemotherapy remains the standard of care.

Background: Patients with extensive-stage small cell lung cancer (ES-SCLC) often develop brain metastases. There is significant controversy regarding the benefit of prophylactic cranial irradiation (PCI) for patients with ES-SCLC. Our objective is to identify ES-SCLC patients who might be most likely to benefit from PCI. Methods: We retrospectively reviewed 173 patients with ES-SCLC treated between 2010–2015. Of these, 117 patients were initially diagnosed without brain metastases and received systemic chemotherapy. Following exclusion of patients who received PCI and less than 2 cycles of platinum doublet therapy, 93 patients remained. Patient records were reviewed for clinical and radiographic features previously identified as relevant risk factors. Primary outcome was brain metastasis-free survival (BMFS). Kaplan-Meier analysis, log-rank tests and Cox multivariate models were used to compare outcomes. Results: Median follow-up was 10.7 months (range, 3–58 months). Thirty-eight (40.9%) patients developed brain metastases. Three or more metastatic sites was associated with inferior BMFS on univariable (1-year estimate 43.8% vs . 61.3%; P=0.020) and multivariable (MVA) analysis [hazard ratio (HR) 2.33, 95% CI: 1.08–5.01; P=0.03). Conclusions: Our results suggest that extracranial metastatic burden is associated with an increased risk for brain metastases in patients with ES-SCLC. As there is no clear standard regarding delivery of PCI in this patient population, utilizing the number of metastatic disease sites as a clinical indicator may help to improve selection of patients who benefit from PCI.