Validation of the 8th TNM classification for small-cell lung cancer in a retrospective material from Sweden

The purpose of this study was to evaluate on a Swedish cohort of small cell lung cancer (SCLC) patients whether the 8th TNM staging system can provide additional prognostic information in comparison with the previous 6th and 7th TNM versions and the older 2-stage LD vs ED system.

We reviewed the medical records of patients (pts) with SCLC diagnosed between January 2008 and February 2016 in the Stockholm and Gotland region. Each patient file was revised and reclassified from the VASGL system to the 6^th, 7^th and 8^th TNM system respectively. We assessed overall survival (OS) according to the T, N, M-descriptor and compared LD/ED with the 6^th, -7^th, -8^th editions of TNM. Four separate multivariate models adjusted for basic patient characteristics were performed.

In total, 706 pts were eligible for the study. Median OS was 7.7 months. Differences in survival between less advanced stages (IA-IIB) were difficult to assess since there were few patients (n = 32). The majority of patients (78%) migrated to new stage categories in the 8th TNM edition; IIIC, IVA and IVB. In the 8th TNM edition subjects with M1a disease had a similar prognosis to patients with multiple metastatic diseases, M1c. Conversely, subjects with a single metastasis had a similar prognosis to M0-disease. On multivariate analysis, stage was an independent prognostic factor independently of the classification system used.

In this cohort, the 8th TNM classification system seems to provide more accurate prognostic information in patients with SCLC when compared to the previous TNM versions. There were few cases with Stages I and II and therefore no robust conclusions can be drawn in this category. The reason single metastatic lesions (M1b) had a better prognosis when compared to M1c could be due to a more aggressive treatment approach in these patients.