Ultrastructural resemblance of basal cell epithelioma to primary epithelial germ.

Six examples of basal cell epithelium were compared to fetal and adult skin. Five parameters were used in this study: abnormally large aggregates of melanosomes in epithelial cells; the paucity of half-desmosomes; the increase of microfilaments in the cell periphery; clustered membrane-limited granules; and desmosome-like structures of stromal fibroblasts. All of these indicators were positive in both basal cell epithelioma and fetal hair follicle; but they were negative in both fetal and adult epidermis. Therefore, it was concluded that basal cell epithelioma seems to mimic fetal primary epithelial germ. Interestingly, stromal fibroblasts of basal cell epithelioma phagocytize collagen fibers, and membrane-limited granules were found both inside and outside the tumor cells facing the digested collagen stroma. In view of the collagenolytic activity of the homogenate of basal cell epithelioma, membrane-limited granules might represent zymogen granules for collagenases.