An ultrastructural study of mucoid carcinoma of the breast: variability of cytoplasmic features.

The ultrastructural characteristics of 14 cases of mucoid carcinoma of the breast, with different histological appearances, have been examined. Thirteen of the tumours were observed to consist of two populations of tumour cells, one showing secretory changes while the other group showed no evidence of activity. In one tumour only synthetically active cells were observed. Ultrastructurally, six different types of cytoplasmic granules, comprising typical mucin plus glycoprotein or protein-containing granules, were identified within the synthetically active tumour cells. The number of types of granules and the relative proportion of the various granules varied between tumours with only mucin granules present in all tumours. It would appear that synthetic pathways are activated in certain tumours which result in protein/glycoprotein granules associated with the argyrophilia observed histologically. In addition, the tumours varied with respect to luminal differentiation, presence of intracytoplasmic lumina, intracytoplasmic mucin pools, lipid droplets, ciliated cells and areas of calcification. The marked heterogeneity of the ultrastructural features of the mucoid carcinoma of the breast prevents the tumours from being readily divided into distinct subgroups.