Lobular carcinoma in situ. Some ultrastructural observations

Bilateral, multifocal areas of lobular carcinoma in situ in the breast of two women were examined by electron and light microscopy. A striking dilatation of the Golgi apparatus was observed in the hyperplastic epithelial tumor cells which contained granular material of varying electron density within the cisternae, suggesting a secretory and/or concentrating activity. Abundant tumor cells filled the dilated mammary ductules leaving small, irregular luminal renants and occasional “pseudo‐intracytoplasmic” lumens. The tumor cells related to each other by an intricate system of microvilli and well‐defined desmosomes; however, large intercellular cisternae were observed in some areas as if the cells had lost cohesiveness. Well‐defined myoepithelial cells at the periphery of the dilated ductules revealed vacuolation, and fragmentation of the cytoplasm. It is possible that lobular carcinoma in situ is mostly an epithelial lesion; the myoepithelial cells are not participating in the neoplastic process and they seem to be crowded and compressed by the proliferating tumor cells against the basement lamina.