A scanning and transmission electron microscopic study of pulmonary adenocarcinoma with histological correlation.

The three-dimensional growth pattern and cell shape and surface of 26 adenocarcinomas of the lung were studied by scanning electron microscopy. The prevailing subtype according to the WHO histological classification, grade of differentiation and secretion of mucosubstances were determined by light microscopy, the tumour cells being further characterized by transmission electron microscopy. The series included 5 acinar, 12 papillary, 1 bronchiolo-alveolar and 8 solid subtypes of adenocarcinoma. Out of these 5 acinar, 9 papillary and 1 bronchiolo-alveolar carcinomas were well or moderately, and 1 solid carcinoma was moderately differentiated. One acinar, 2 papillary and 7 solid carcinomas were poorly differentiated. All tumours secreted mucosubstances, which in the solid carcinomas occurred as intracytoplasmic vacuoles. In acinar adenocarcinomas there were columnar tumour cells surrounded by fibrotic stroma. In the papillary and bronchiolo-alveolar subtypes the tumour cells formed papillary nodules along the alveolar walls while the solid subtype showed no organized structures. The tumour cells were mostly cylindrical or club-shaped in well and moderately differentiated and spherical in less differentiated neoplasms. In well differentiated papillary carcinomas the tumour cells were tightly attached to each other, whereas many moderately and all poorly differentiated carcinomas had broad intercellular spaces. Tumour cells with microvilli occurred more often in the acinar, papillary and bronchiolo-alveolar subtypes, which were mostly well or moderately differentiated, than in the mostly poorly differentiated solid subtype of pulmonary adenocarcinoma, which often had a rough apical surface with microridges. In conclusion the three-dimensional growth pattern corresponded fairly well with the prevailing histological subtype and the surface structure of cancer cells seemed to reflect the grade of differentiation in pulmonary adenocarcinomas.