Prognostic stratification of T1 lung adenocarcinoma with micropapillary or solid patterns: a cohort study

The impact of micropapillary and/or solid (MP/S) patterns on prognostic stratification within T1 subcategories (T1a-b and T1c) is uncertain. We aimed to evaluate the prognostic stratification of combined MP/S status and tumor size, and to compare the outcomes of micropapillary and/or solid positive (MP/S⁺) T1 tumors with those of higher T categories.

We examined 586 patients who underwent curative resection for stage I invasive lung adenocarcinoma from January 2018 to December 2019. We compared survival outcomes among T1 subcategories classified by MP/S. The primary endpoints were overall survival (OS) and recurrence-free survival (RFS). Kaplan-Meier method was used to estimate survival, and log-rank tests were used to compare the two groups.

Among 586 patients, 184 (31.4%) were MP/S⁺, and 402 (68.6%) were micropapillary and/or solid negative (MP/S^-). In total, there were 345 (58.9%) T1a-b, 155 (26.5%) T1c, and 86 (14.7%) T2a. In T1a-b tumors, MP/S⁺ status was significantly correlated with poorer outcomes, with survival rates similar to those of T1c MP/S^- cases [RFS: hazard ratio (HR) 0.89, 95% confidence interval (CI): 0.37-2.13, P=0.79; OS: HR 0.74, 95% CI: 0.25-2.21, P=0.60]. In T1c tumors, MP/S⁺ was associated to much higher risks of recurrence and death. The outcomes for T1c MP/S⁺ were similar to those for pathologic T2a (RFS: HR 1.01, 95% CI: 0.54-1.88, P=0.98; OS: HR 0.87, 95% CI: 0.39-1.94, P=0.73).

MP/S patterns indicate higher-risk subgroups within T1 lung adenocarcinoma. Incorporating MP/S status into postoperative risk evaluation may enhance prognostic accuracy.