Prognostic significance of the 8th edition of the TNM classification for patients with extensive disease small cell lung cancer

Background: Small cell lung cancer (SCLC) is typically categorized according to disease extent as limited or extensive, and utility of the 8th TNM classification, recommended for lung cancer staging, which demonstrates a strong association with non-small-cell lung cancer (NSCLC) management, remains unclear. Methods: This retrospective study included 277 consecutive SCLC patients treated at a single institution between 2008 and 2016. Results: According to the currently used two-stage system, 186 (65.7%) of the patients were classified as having extensive disease (ED)-SCLC. Among the ED-SCLC patients, ten (5.3%), 38 (20.4%), 32 (17.2%), and 106 (57.0%) were categorized into stages M0, M1a, M1b, and M1c, respectively, according to the 8th TNM classification. There was a significant difference in overall survival based on the M descriptors: 15.8 (95% CI 9.4-22.2) months in the M1b group vs 7.3 (95% CI 5.7-8.9) months in the M1c group (P<0.001). Multivariate analysis showed that in addition to the known prognostic factors such as performance status, serum albumin and lactate dehydrogenase, M descriptor was a prognostic factor (HR 1.95, 95% CI 1.38-2.77; P<0.001). Conclusion: The 8th INM classification has a prognostic value in SCLC. Similarly to NSCLC treatment approaches should be considered on the basis of the 8th TNM classification, especially stage IVA separate from stage IVB in ED-SCLC patients.