The ratio of cancer cells to stroma within the invasive area is a histologic prognostic parameter of lung adenocarcinoma

•Low proportion of cancer cells in the invasive area had better prognosis.•This was associated with the greater proportion of VVG-positive elastic fibers.•The character of the invasive area could be a useful histologic prognostic parameter. This study evaluated whether the proportion of cancer cells to non-cancerous stroma within the invasive area is associated with the prognosis of patients with lung adenocarcinoma. A total of 127 patients with lung adenocarcinomas with tumors larger than 3 cm in total size were enrolled in this study. We classified the tumors according to the ratio of area occupied by cancer cells within the invasive area (Type A: more than 50% of the invasive area, Type B: 10–50%, and Type C: less than 10%) and analyzed the clinicopathological differences between Types A, B, and C. The invasive size of Type A tumors (n = 35) was significantly larger than those of the other two tumor types; however, there was no significant difference in the invasive size between Types B (n = 65) and C (n = 25) tumors. The recurrence-free survival time of patients with Type C tumors was significantly longer than those of patients with Type A and B (P