Comparison of Malignant Grade Between Pure and Partially Invasive Types of Early Lung Adenocarcinoma

Background The present study investigates the malignant significance of lepidic component presence in predominantly invasive lung adenocarcinoma that comprise less than 50% lepidic growth of the tumor. Methods Among 347 consecutive patients with completely resected clinical stage IA lung adenocarcinoma, we excluded those with adenocarcinoma in situ, minimally invasive, and lepidic predominant invasive adenocarcinoma. We finally assessed 167 patients with predominantly invasive lung adenocarcinoma. We analyzed the clinicopathologic characteristics and prognoses of patients with 49 pure invasive tumors without lepidic growth and 118 partially invasive tumors with lepidic growth. Results Pure invasive tumors were associated with being male, small tumor size, high maximum standardized uptake, and pleural as well as lymphatic invasion. Nonetheless, the invasive component size of both tumor types was similar. The predominant subtypes of pure and partially invasive tumors, respectively, were papillary, 17 (34.7%) and 53 (44.9%); acinar, 10 (20.4%) and 51 (43.2%); solid, 19 (38.8%) and 11 (9.3%), and micropapillary 3 (6.1%) and 3 (2.5%; p < 0.001). Recurrence-free survival was significantly worse for patients with pure, compared with partially, invasive tumors ( p = 0.045). Conclusions Among predominantly invasive stage IA lung adenocarcinomas, the malignant potential was higher for pure invasive tumors, and the prognosis was poorer than for partially invasive tumors when the invasive components were of equal sizes. The presence or absence of a lepidic component reflects a difference in subtype predominance and can help to decide the malignant grade of lung adenocarcinoma.