Comparative study of clinicopathological characteristics and prognosis between combined and pure small cell lung cancer (SCLC) after surgical resection.

Background: Histologically, SCLC are classified as pure (P-SCLC) and combined subtypes (C-SCLC). Currently, few studies compare the clinicopathological characteristics and explore the treatment strategies applied to them.

Methods: Between July 2005 and April 2016, the clinical records of 297 postoperative patients with pathologically confirmed SCLC were retrospectively analyzed. Kaplan-Meier method and Cox regression model were separately used for stratified univariate and multivariate survival analysis.

Results: A total of 46 cases (15.5%) of C-SCLCs and 251 cases (85.5%) of pure SCLCs (P-SCLCs) were included in this study. The average age of C-SCLCs was a little higher than that of P-SCLCs (59.65 ± 8.72 vs. 56.56 ± 10.12; P = 0.053). More patients had a history of smoking in C-SCLC (78.3% vs. 63.3%; P = 0.074). The five-year overall survival (OS) rate for P-SCLCs and C-SCLCs was 65.1% and 56.7%, respectively (P = 0.683). For P-SCLC, stage and an intervention of prophylactic cranial irradiation (PCI) were independent factors that affected OS. In C-SCLCs cases, performing sublobectomy was an independent risk factor for poor prognosis.

Conclusions: We identified no significant difference in clinical characteristics and outcome between C-SCLCs and P-SCLCs. However, the factors affecting the prognosis of the two subtypes were slightly inconsistent. For C-SCLCs, the extent of resection had a greater impact on survival, and lobectomy combined with systemic lymph node dissection should therefore be performed as extensively as possible. In addition, PCI was beneficial in improving the SCLC OS rate.

Key Points: This study demonstrated the prognosis of C-SCLCs did not significantly differ from that of P-SCLCs, but was more susceptible to the extent of resection. Patients with C-SCLC who underwent limited resection had a significantly increased risk of shorter OS. This study highlighted the importance of performing lobectomy for resectable C-SCLC patients. This study also proved the benefit of PCI in improving the OS rate for both P-SCLC and C-SCLC patients.