33 Special Types of Invasive Breast Carcinoma: Diagnostic Criteria ...

ubbery, and can mimic carcinoma grossly. They have a biphasic cytoarchitecture
composed of tubular structures lined by duct luminal epithelial cells surrounded by
myoepithelial cells that have spindle cell or polygonal cell shapes (often with clear
cytoplasm). The myoepithelial cells may predominate, necrosis may be present, and
mitotic activity can be brisk, measuring up to 10 mitotic figures per 10 high-power
fields. Because of the marked differences in tumor aggressiveness and therapy, typical
adenomyoepithelioma should be clearly distinguished from the spindle cell variant of
metaplastic breast carcinoma. Moreover, closely related examples of "malignant
myoepithelioma" or "myoepithelial carcinoma" or "adenomyoepithelioma with
undifferentiated carcinoma" are scattered throughout the literature (38-42). A peculiar
DCIS variant has been described that is characterized by the intraductal growth of
carcinoma cells having clear cell and spindle cell myoepithelial differentiation (111).
Myofibroblastoma of breast, a tumor showing myofibroblastic differentiation without
epithelial features, simulates spindle cell adenomyoepithelioma and other spindle
tumors of the breast (112). Myofibroblastomas have a predilection for occurring in
men, but they are benign tumors in either sex. Immunoreactivity for S-100 protein and
cytokeratin was absent in the 10 tumors examined, but desmin immunoreactivity was
focally present in three lesions. Others have reported examples of myofibroblastoma
that have been vascular and/or having infiltrating borders. Cellular examples of the
angiolipoma of the breast could also simulate the spindle-cell carcinoma and even
angiosarcoma (113); and don’t forget, spindle-cell and atypical lipomas can occur in
the breast rarely simulate other spindle-cell tumors.
Pseudoangiomatous hyperplasia (PASH) of mammary stroma is a benign proliferation
of keloidlike fibrosis within which there are slitlike pseudovascular spaces. Its main
importance is in its similarity to low-grade angiosarcoma (114, 115). The importance
of distinguishing PASH from angiosarcoma may have become even greater because
there are recent reports of the development of secondary angiosarcoma after tylectomy
and postoperative radiation therapy and after segmental mastectomy complicated by
lymphedema (116, 117).
The criteria for breast hamartoma remain somewhat unclear, but its recognition
currently depends on the combination of clinical, radiologic, and pathologic criteria. It
represents growth malformation of normal breast tissues in a dysmorphic or abnormal
configuration. It presents as a breast mass and exhibits diverse appearances, which
include an admixture of epithelial and stromal elements. Stromal elements may show
extensive PASH changes. The stroma usually includes mature fat (118-121). A
reproducible morphologic distinction of this process from circumscribed fibrocystic
disease and fibroadenoma has yet to be achieved. Myoid hamartoma is a form of
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