Clinicopathology of stromal invasion in lung adenocarcinoma

In the World Health Organization classification, lung adenocarcinoma with mixed subtypes is defined as invasive carcinoma with evidence of vascular, pleural, or stromal invasion. The histological criteria for stromal invasion, however, are not clearly established. A total of 157 peripheral pure bronchioloalveolar carcinoma (BAC) or lung adenocarcinoma with mixed BAC and others were reviewed. All cases had been resected between 1986 and 2000 and measured < or =30 mm in maximum dimension. Destruction of alveolar framework (DAF) was defined as distortion or discontinuity of the alveolar framework by tumor growth. The extra-alveolar area involvement (EAAI) was defined as tumor growth outside the alveolar framework, which includes the following areas: bronchial wall, perivascular connective tissue and/or the vascular wall, interlobular septum and the visceral pleura. Survival of patients with adenocarcinoma without DAF (n = 41) was 100%. Even when adenocarcinoma involved DAF and lacked EAAI (n = 21), survival was 100%. The 5 year survival rate of groups with two invasion signs (n = 34) was 90.1%, and that of groups with three to five invasion signs (n = 61) was 66.7%. Tumor growth outside the alveolar framework is the hallmark of stromal invasion.