Morpho-functional differentiation in lobular carcinoma of the breast.

Lobular carcinoma of the breast has been studied using histochemical methods for mucosubstances; immunocytochemical methods for casein and actin; the ruthenium red electronycytochemical method for acid glycoproteins and an immunoelectroncytochemical method for casein. Mucosubstances and casein showed a similar cytoplasmic localization, but casein production was much more intense and also showed a more diffuse cytoplasmic localization. Occasionally casein assumed the form of target-like 'inclusions' as seen characteristically with the mucosubstances. The neoplastic cells were not stained by antisera against actin. Ultrastructurally, some cells showed an intracytoplasmic lumen with microvilli and/or an irregular outline at one extremity which was covered by microvilli. An electron-dense 'fuzz' and casein coated the microvilli of cells exposed respectively to ruthenium red and an anticasein serum followed by peroxidase--anti-peroxidase complexes. It is concluded that lobular carcinoma shows evidence of epithelial rather than myoepithelial differentiation with the emphasis on epithelial secretory cells engaged in intensive milk protein production. All 10 tumours tested for oestrogen receptors were positive in contradistinction to ductal carcinoma with a lower incidence of positivity. It appears that, in addition to distinctive histological and histochemical features, lobular carcinoma has an almost constant endocrine pattern in respect of its oestrogen receptor content.