Detection of early invasion on the basis of basement membrane destruction in small adenocarcinomas of the lung and its clinical implications

To evaluate the correlation between the degree of basement membrane (BM) preservation and clinicopathological characteristics in the replacement-growth type (lepidic growth type) of small peripheral adenocarcinomas of the lung, the BM components of 72 surgically resected. replacement-growth type adenocarcinomas of the lung, 2 cm or less in diameter, were evaluated immunohistochemically by using a monoclonal antibody to Type IV collagen and polyclonal antibodies to 7S collagen and laminin. The tumors were classified into the following three distinctive histological types according to the condition of the elastic framework. Type I, bronchioloalveolar carcinoma without fibrotic foci; Type II, sclerosing bronchioloalveolar carcinoma without elastic framework destruction; and Type III, sclerosing bronchioloalveolar carcinoma with elastic framework destruction. The BM was well preserved in the area of bronchioloalveolar spread along fully expanded alveoli in all tumor types; however, BM preservation was significantly lost in the areas of collapsed alveoli in Type III tumors. There were no BM component staining reactions in the scarred regions of Type III tumors. In addition, lymph node metastasis was significantly greater in Type III tumors and BM-destroyed tumors. We concluded that the BM was largely destroyed by tumor cell invasion in the scarred region of Type III adenocarcinomas. Type III tumors had discontinuous BMs in the area of collapsed alveoli, indicating that this BM-destructive pattern must be the first step in tumor invasion. Type I and II tumors were concluded to be noninvasive adenocarcinomas, because their BM components were well preserved and they had a good outcome.