Histological subtypes or grading of pulmonary adenocarcinoma. A histochemical and electron microscopic study

To reveal whether the different histological subtypes of pulmonary adenocarcinoma are composed of different types of cells, we analyzed basic mucus histochemistry and ultrastructural features in a series of 61 adenocarcinomas correlating the findings with four ways of histological classification and grading. 82% of the tumours were composed of a single and 18% of two or more cell types. The original WHO classification had no association with the histochemical or ultrastructural features studied. A modified WHO classification, however, based on the prevailing subtype, had significant associations with five, a classification based on prevailing growth pattern with four, and histological grading with eight histochemical and electron microscopic features. The results suggest that it is more important to classify pulmonary adenocarcinomas by histological grades than by subtypes.