Comparative ultrastructure of tubular carcinoma and sclerosing adenosis of the breast.

The innocuous histologic appearance of tubular carcinoma of the breast and its superficial histologic resemblance to sclerosing adenosis will occasionally present diagnostic problems. A comparative ultrastructural analysis of two tubular carcinomas and three cases of sclerosing adenosis was made that showed definite differences in the pattern of myoepithelial cell differentiation and basal lamina deposition in these two entities. Prominent myoepithelial cells and basal lamina reduplication were both conspicuous features of sclerosing adenosis that appeared to be absent in tubular carcinoma. Intracytoplasmic "pseudocysts" were frequently found in sclerosing adenosis, but not in tubular carcinoma. Conversely, intracytoplasmic lumina and incomplete tubular structures were present in tubular carcinoma and seemingly absent in sclerosing adenosis. Such basic ultrastructural differences may help to differentiate these two mammary lesions when diagnostic problems occur at the conventional light microscopic level.