Residual tumor descriptors proposed by the International Association for the Study of Lung Cancer may not be applicable to stage I and ground-glass opacity-featured non-small cell lung cancer.

Background: The International Association for the Study of Lung Cancer (IASLC) has proposed a residual tumor descriptor, essential for subsequent treatments. This study aimed to validate the prognostic effect of the proposed R descriptor and restrict its scope of clinical application in a large-scale cohort with non-small cell lung cancer (NSCLC).

Methods: Patients, who underwent lobectomy from January 2010 to May 2019, were retrospectively reviewed. Patients were categorized according to the different R classification standards proposed by Union for International Cancer Control (UICC) and IASLC.

Results: Among 5,200 enrolled patients with NSCLC, 1,727 and 9 cases of UICC-R0 were re-evaluated as uncertain resection [R(un)] and R1, respectively. After reclassification, there were 3,228 (62.1%) cases of R0, 1,727 (33.2%) cases of R(un), 151 (2.9%) cases of R1, and 94 (1.8%) cases of R2. Not performing rigorous systematic nodal dissection (SND) or lobe-specific SND (68.3%) was the main reason for the alteration from R0 to R(un). Patients with R(un) showed intermediate survival between those with R0 and R1. Further multivariable Cox analysis indicated that the proposed R descriptor was an independent prognostic factor for overall survival (OS) and recurrence-free survival (RFS). However, subgroup analysis of OS and RFS revealed that there was no significant difference between R0 and R(un) in patients with ground-glass opacity (GGO) or patients with tumor-node-metastasis stage I.

Conclusions: R(un) represented an intermediate type between R0 and R1. Our study provided an external validation for new residual tumor descriptors for NSCLC proposed by IASLC. Proposed residual tumor descriptors were applicable in radiologic solid NSCLC and stage II-III NSCLC, but were ineffective for GGO-featured or stage I NSCLC.