Vascular Invasion in Peripheral Lung Adenocarcinoma Related to Stromal Formation

Abstract

Twenty-two surgically resected peripheral lung adenocarcinomas of the non-mucus producing type which measured less than 3 cm in diameter and showed definite vascular invasion were studied histologically. Vascular invasion was defined as definite tumor cell embolization in the vascular lumen on H&E and Elastica van Gieson staining. Tumor stroma was divided into two areas of central fibrosis and replacement growth around the central fibrosis. The central fibrotic area was divided into three types according to the patterns of elastotic framework formation as follows; 1) areas with preserved air spaces with thick elastotic walls, 2) areas without preserved air spaces because of collagenized elastosis or 3) areas of collapsed elastosis. Vascular invasion was detected at 35 sites of replacement growth in 15 cases, 15 sites of Type 1-like elastotic framework in 11 cases, 13 sites of collagenized elastotic framework in 11 cases, and 2 sites of collapsed elastotic framework in one case. It was generally found at the boundary between central fibrosis and the replacement growth. Vascular lesions seen within central fibrosis tended to show occlusive or destructive changes rather than vascular invasion. Vascular invasion in peripheral lung adenocarcinomas may occur in association with angiogenesis caused by tumor invasion, while tumor-specific stroma of central fibrosis is formed, and then is seen more peripheral to central fibrotic area or in replacement growth with progress in collagenization of central fibrosis.