Clinicopathological Difference and Survival Impact of Patients with c-SCLC and SCLC

Combined small cell lung cancer (c-SCLC) distinguishes itself from small cell lung cancer (SCLC) due to its inclusion of both SCLC and non-small cell lung cancer (NSCLC) components. Few studies have compared clinicopathological characteristics, prognosis and factors affecting survival. We therefore addressed the issues in this study.

A total of 400 c-SCLC and 20,841 SCLC patients were enrolled using SEER database. Difference in clinicopathological characteristics of SCLC and c-SCLC patients was analyzed using chi-square. Kaplan-Meier was applied to compare their survival before and after propensity score matching (PSM). Cox regression model was adopted to assess the impact of different clinical variables on survival. Logistic regression was applied to identify risk factors for c-SCLC and SCLC patients.

Differences in race, sex, T stage, N stage, surgery, bone, brain and liver metastasis were detected between c-SCLC and SCLC patients. c-SCLC patients had better overall survival (OS) than SCLC patients before PSM. Age, race, sex, T stage, N stage, surgery, bone, brain, liver and lung metastasis were prognostic factors affecting OS for c-SCLC and SCLC (P < 0.05). However, a significant OS benefit was not observed in c-SCLC after adjusting for clinicopathological variables (HR, 0.950; 95% CI, 0.842-1.073; P=0.411). No significant OS difference was found between c-SCLC and SCLC patients after PSM (P = 0.789). c-SCLC patients had lower risk of lymph node (OR: 0.555; 95% CI: 0.439-0.703; P < 0.001) and liver metastasis (OR: 0.591; 95% CI: 0.448-0.779; P < 0.001), whereas had no significant differences in bone and brain metastasis risks (P > 0.05) compared with SCLC patients.

The prognosis of c-SCLC did not significantly differ from that of SCLC if clinicopathological characteristics are controlled. Better prognosis for c-SCLC patients over SCLC patients may be ascribed to fewer liver and lymph node metastases upon diagnosis.