Is the size of the lepidic component negligible when measuring the size of the tumor to determine the stage of lung adenocarcinoma?

Background: After applying the 8th edition of the TNM staging system, the invasive component size, not total tumor size, began to be used as a T descriptor for the stage. The aim of this study was to evaluate whether the size of the lepidic component can be negligible when using only the invasive component size as the T descriptor. Methods: From 2010 to 2018, 613 consecutive patients were diagnosed as having stage IA lung adenocarcinoma and underwent anatomical lobectomy at a tertiary hospital. Pathologic specimens and medical records were reviewed retrospectively. Statistical analyses were conducted to find out whether the recurrence of stage IA lung adenocarcinoma was more affected by total tumor size (including lepidic component size) or invasive component size. Results: The 5-year recurrence-free survival (RFS) rates of stage 0, stage IA1, stage IA2, and stage IA3 were 100%, 98.4%, 89.1%, and 81.7%, respectively. In multivariate analysis, total tumor size was not a risk factor for recurrence, whereas invasive component size was a significant risk factor for recurrence (Hazard ratio = 1.658, P=0.043). In subgroup analysis, 5-year RFS rates of large lung adenocarcinoma (total tumor size >3 cm) and others (total tumor size <= 3 cm) in the same invasive component size group (stage IA2 and stage IA3) were not statistically different. Conclusions: Invasive component size was a risk factor for recurrence of stage IA lung adenocarcinoma, while total tumor size was not a risk factor. Therefore, it seems to be appropriate to ignore the size of the lepidic component.