The prognostic utility of the histologic subtype of stage I lung adenocarcinoma may be diminished when using only the invasive component to determine tumor size for tumor node metastasis (TNM) staging

BACKGROUND: Histologic subtypes were considered prognostic factors in early-stage lung adenocarcinoma in the 7(th) edition of the tumor node metastasis (TNM) staging system (TNM-7). However, the T-staging system has changed and now measures only the size of the invasive component to determine tumor size. The aim of this study was to determine whether the histologic subtype is still a prognostic factor in the 8(th) edition of the TNM staging system (TNM-8). METHODS: From 2010 to 2017, 788 patients who underwent curative surgery for stage I lung adenocarcinoma according to TNM-8 were analyzed retrospectively. Survival rates were compared among predominant patterns of adenocarcinoma. Prognostic factors were analyzed according to risk factors for recurrence in stage I lung adenocarcinoma. RESULTS: The 5-year recurrence-free survival rates among predominant histologic subtypes were statistically different, especially between the lepidic/acinar/papillary group and the micropapillary/solid group. Total tumor size was not significantly different between the two groups, but invasive component size was different (1.5 vs. 2.3 cm, P<0.001). In the multivariate analysis that adopted total tumor size as a variable, visceral pleural invasion (VPI), lymphovascular invasion (LVI), and micropapillary-predominant adenocarcinoma were significant predictors for recurrence. Conversely, adenocarcinoma subtypes were not significant risk factors for recurrence in the multivariate analysis that adopted invasive component size as a variable. CONCLUSIONS: The importance of adenocarcinoma subtype for prognosis may be reduced when only the invasive component of a tumor is used to determine tumor size, as described in the TNM-8 staging system.