Visceral pleural invasion in T1 tumors (≤3 cm), particularly T1a, in the eighth tumor-node-metastasis classification system for non-small cell lung cancer: a population-based study.

Background: We aimed to validate the tumor (T) descriptors of visceral pleural invasion (VPI) for T1 tumors (<3 cm) in the 8th edition of the tumor-node-metastasis (TNM) classification system and the prognostic value of VPI for resected T1a tumors.

Methods: The external cohort consisted of 23,501 patients with resected pN0 non-small cell lung cancer (NSCLC) selected from the Surveillance, Epidemiology, and End Results (SEER) database (2010 to 2013). The classification of T1 tumors with VPI was investigated using survival curves. The internal cohort consisted of patients diagnosed with pN0 NSCLC between 2011 and 2013 at Guangdong Lung Cancer Institute. The prognostic value of VPI for T1a tumors (<1 cm) was further assessed in these two cohorts.

Results: The overall survival (OS) and lung cancer-specific survival (LCSS) of the T1-VPI group and groups of each T stage (size only) were compared in the external (SEER) cohort. There were no significant survival differences between the T1-VPI and T2a groups (OS: P=0.706; LCSS: P=0.792) and T1-VPI and T2b groups, although the latter showed a trend toward lower P-values (OS: P=0.117; LCSS: P=0.094). In the internal cohort, a significant difference in OS was observed between patients with T1-VPI and those with T2b (P=0.049). Among patients with T1a tumors and VPI in the SEER database, the prognosis of the non-sub-lobectomy group was superior to that of the sub-lobectomy group, with intrathoracic recurrence as the predominant relapse pattern of T1 tumors with VPI (69.2%).

Conclusions: T1 tumors (<3 cm) with VPI can be staged as T2a in the 8th TNM staging system and surgical resection of T1a tumors is a concern when VPI is present.