Objective: Lung adenocarcinomas 2 cm or less in diameter were studied to develop histologic criteria predicting the outcome. MATERIALS and Methods: We reviewed 510 consecutive lung adenocarcinomas 2 cm or less in diameter and assessed three histologic parameters to implement a histologic scoring system: lymphovascular invasion, maximum diameter of the nonbronchioloalveolar carcinoma (BAC) component, and percentage of the solid, cribriform, and/or papillary component in the entire tumor volume (%solid/cribriform/papillary). One point was given to each of lymphovascular invasion-positive, non-BAC >10 mm and %solid/cribriform/papillary 30%, and by the sum of these points, a score of 0 to 3 was assigned for each tumor. We also evaluated minimally invasive adenocarcinomas comprising non-BAC 5 mm, Sakurai grades 1 and 2. Results: Five-year disease-free survival rates of 287 patients with a histologic score of 0, 69 with a score of 1, 64 with a score of 2, and 90 with a score of 3 were 98.9%, 92.4%, 78.4%, and 54.0%, respectively. The 510 tumors included 129 noninvasive and 127 minimally invasive adenocarcinomas. None of these tumors recurred. In remaining 254 patients with overtly invasive adenocarcinomas, 5-year disease-free survival rates in 51 with a histologic score of 0, 49 with a score of 1, 64 with a score of 2, and 90 with a score of 3 were 95.9%, 89.2%, 79.4%, and 54.2%, respectively. Conclusion: The histologic scoring system comprising lymphovascular invasion-positive, non-BAC >10 mm and %solid/cribriform/papillary 30% is able to predict the outcome of lung adenocarcinomas 2 cm or less in diameter not only in all cases but also in overtly invasive adenocarcinomas. Minimally invasive adenocarcinomas did not recur in this large series.
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