The role of prophylactic cranial irradiation in surgically resected combined small cell lung cancer: a retrospective study

Background: Combined small cell lung cancer (C-SCLC) is defined as small cell lung cancer (SCLC) combined with any of non-small cell lung cancer (NSCLC) histological types, such as large cell carcinoma, squamous cell carcinoma, or adenocarcinoma. Since C-SCLC is an increasingly recognized subtype of small cell carcinoma, we conducted a retrospective study in our institution to explore the value of prophylactic cranial irradiation (PCI) in patients with C-SCLC treated by surgery. Methods: Between 2005 and 2014, the records of all consecutive patients with pathologically diagnosed C-SCLC after surgery in our institution were reviewed. Overall survival (OS), disease-free survival (DFS), and brain metastasis free survival (BMFS) were estimated by Kaplan-Meier method. Survival differences were evaluated by log-rank test, while multivariate analysis was performed by a Cox proportional hazards model. Results: Of the total 91 patients included in this analysis, 11 patients (12.1%) were in PCI group and 80 (87.9%) in non-PCI group. The 5-year cumulative incidence of brain metastasis in the whole group was 22.2% (26.3% in non-PCI group vs. 0% in PCI group), and 5-year OS rate was 44.1%. Patients treated with PCI had significantly longer OS (P=0.011) and DFS (P=0.013), also had the trend to live a longer BM.FS with marginal significance (P=0.092) than non-PCI-treated patients. The multivariate analysis showed that PCI [hazard ratio (LIR) =0.102, P=0.024] was one of independent prognostic factors of the OS in surgery-treated C-SCLC patients. Conclusions: C-SCLC patients have a relative high risk of developing brain metastases based on our study. These data showed that PCI could improve OS and DFS, as well as tend to decrease brain metastases in surgically resected C-SCLC. However, whether PCI could be part of comprehensive treatment modalities in C-SCLC should be assessed in prospective studies.