Two women, aged 82 and 58 years old, cases 1 and 2, respectively, with the
non-tubular and matrix-producing variant of malignant adenomyoepithelioma (
MAM) of the breast are described. The tumors were 20 and 35 mm in diameter,
respectively, and had cut surfaces with a tan-white-colored appearance and
vague lobulation. Although both tumors showed marked central necrosis and
a high level of mitoses, the tumor cells had relatively monomorphous nuclei
and exhibited only mild atypia. The invasive component was predominantly t
rabecular and lobular, and the intraductal component demonstrated a focal-c
omedo pattern. The cytoplasm of the tumor cells was rather scanty, vacuolar
or pale with ill-defined borders. The tumor in case 2 contained intermingl
ed spindle-shaped cells. The stroma of both tumors resembled that of pleomo
rphic adenoma, containing a myxoid and chondroid matrix and, in case 2, car
tilage and mature bone. Immunohistochemical and ultrastructural analyses of
both tumors revealed dual cytological differentiation, predominantly of my
oepithelial cells with secretory epithelial cells intermingled haphazardly.
Although these tumors resembled metaplastic carcinomas, particularly matri
x-producing carcinomas, they showed marked myoepithelial differentiation wi
thout overt tubular differentiation, a pattern quite different from matrix-
producing carcinomas and from the adenomyoepitheliomas reported so far. MAM
of the breast, non-tubular and matrix-producing variant, resembles epithel
ioid myoepithelial carcinoma of the salivary gland and has not been reporte
d previously in the English literature.