Implications of the Eighth Edition of the TNM Proposal: Invasive Versus Total Tumor Size for the T Descriptor in Pathologic Stage I-IIA Lung Adenocarcinoma.

INTRODUCTION: The eighth edition of the TNM staging system included the proposal that the T descriptor be determined according to the invasive component, excluding lepidic component, for nonmucinous lung adenocarcinomas. We sought to conduct a clinicopathologic comparative analysis of the newly proposed classification using invasive size versus total tumor size. METHODS: Patients who underwent lung resection for primary lung adenocarcinoma with pathologic stage (p-Stage) I-IIA (based on total size [t]) were reviewed (n = 1704). Pathologic invasive size was measured, and tumors were reclassified using invasive size (i). Cumulative incidence of recurrence and lung cancer-specific cumulative incidence of death were analyzed using a competing-risks approach. Prognostic discrimination by p-Stage(t) and p-Stage(i) was evaluated using a concordance index (C-index). RESULTS: The use of invasive size resulted in downstaging in 377 of 1704 patients (22%), with twice as many patients with p-Stage IA1 (IA1[i] versus IA1[t]: 389 [23%] versus 195 [11%]). However, outcomes were similar between the two groups (IA1[i] versus IA1[t]: 5-year cumulative incidence of recurrence, 11% versus 13%; 5-year lung cancer-specific cumulative incidence of death, 5% versus 7%). Prognostic discrimination by p-Stage(i) was better than by p-Stage(t) (C-index for p-Stage[i] versus p-Stage[t]: recurrence, 0.614 versus 0.593; lung cancer-specific death, 0.634 versus 0.621). CONCLUSIONS: When invasive size, rather than total size, was used for the T descriptor, a larger number of patients were classified with a favorable prognosis (p-Stage IA1) and better prognostic discrimination of p-Stage I-IIA nonmucinous lung adenocarcinomas was achieved.