Prognostic significance of the 9th TNM lung cancer staging system in SCLC

Clinical research and decision-making for small cell lung cancer (SCLC) are still based on the dichotomous classification of limited-stage disease or extensive-stage disease. This study aimed to evaluate the prognosis of the 9th edition of the tumor-node-metastasis (TNM) classification for SCLC in a real-world setting.

This retrospective study included SCLC patients diagnosed between January 2014 and December 2021 in our center. Patients who had undergone complete staging evaluation were re-staged according to the 8th and 9th editions of the TNM classification for lung cancer. Kaplan-Meier analysis was conducted to determine overall survival (OS). Univariate and multivariate analyses were performed using the Cox proportional hazards model to assess the prognostic impact of the relevant factors.

A total of 1,329 patients were included in the study. All patients underwent clinical staging, while pathological staging was available on 51 patients. After a median follow-up of 39.67 months [95% confidence interval (CI): 36.28-43.06], the median OS was 15.40 months (95% CI: 14.45-16.35). According to the 8th and 9th TNM classification, the median OS, 1-, 2-, and 3-year OS rates showed a progressive decline with advancing stage. The median OS of the N_2a and N_2b subclasses that were newly added to the 9th edition was 20.00 months (95% CI: 16.14-23.86) and 14.53 months (95% CI: 12.88-16.18), respectively. The 3-year survival rates were 22.9% and 14.6%, respectively. Patients with N_2b exhibited poorer outcomes (P=0.002). However, compared to M_1c2, the median OS was numerically longer in patients with M_1c1 (11.67 vs. 10.63 months), but it did not achieve a statistically significant difference (P=0.13). Multivariate analysis revealed that both the 8th and 9th editions of the TNM were independent prognostic factors.

This retrospective analysis confirmed a significant difference in prognosis between the N_2a and N_2b subgroups in the 9th edition. No statistically significant difference was observed between the M1c1 and M_1c2 subgroups. The present study suggests that the 9th edition of TNM requires further validation using external datasets, and factors such as the number of metastatic lesions in a single organ may also be included in future TNM classification systems.