Ultrastructure of well-differentiated adenocarcinomas of the lung with special reference to bronchioloalveolar carcinoma.

The cytologic phenotypes of 20 well-differentiated pulmonary adenocarcinomas were determined by electron microscopy. On examination of more than 100 cells in each case, the tumors were classified according to the predominant cell types. Nine cases (45%) were of mucous cell type, further divided into 7 cases of bronchial surface epithelial cell type, 1 case of bronchial gland cell type, and 1 case of metaplastic bronchiolar goblet cell type. The remainder included 5 cases (25%) of Clara cell type, 2 cases (10%) of type II cell type, and 4 cases (20%) of mixed cell type. The predominant histologic pattern by light microscopy was "typically" bronchioloalveolar (Manning et al.'s type 1) in the metaplastic goblet cell tumor and papillary in most Clara cell-type tumors, while it was glandular in bronchial surface and bronchial gland cell types, although variable in type II cell or mixed cell type. Therefore, bronchioloalveolar carcinomas, when histologically defined inclusive of papillary tumors, present cytologic phenotypes also related to the bronchioloalveolar epithelium, i.e., metaplastic goblet or Clara or type II cell subtypes, which is in accordance with some previous reports. These tumors could be distinguished from the other (glandular) adenocarcinomas that show primarily bronchial mucous cell differentiation.