Mucinous Cystadenocarcinoma of the Breast.

We report a case of mucinous cystadenocarcinoma (MCA) of the breast in a 96-year-old woman. This is an extremely rare variant of primary breast carcinoma that bears a striking resemblance to MCAs of the ovary and pancreas. The macroscopic appearance and secretion pattern (cytologic findings) resembled cystic hypersecretory carcinoma. However, microscopically, the epithelial cells were quite different from those of cystic hypersecretory carcinoma. In the present study as well as in the literature, MCAs tend to occur more frequently in elderly women. Immunohistochemical findings suggest that they may develop independently of estrogenic stimulation. Although MCAs show high proliferative activity, the prognosis was favorable in the present case as well as in the reported cases. Because MCAs appear to have a distinct pathogenesis and biologic behavior, they should be distinguished from ordinary mucinous carcinomas, cystic hypersecretory carcinomas, and carcinomas of other histologic subtypes. [ABSTRACT FROM AUTHOR]