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

Another family of salivary gland-type mammary epithelial neoplasms is devoid of
myoepithelial cells. Key examples include mucoepidermoid carcinoma and acinic cell
carcinoma. The number of cases of salivary gland-type mammary neoplasms in the
published data is constantly increasing but some of the rarest subtypes like
polymorphous low-grade adenocarcinoma and oncocytic carcinoma are "struggling" to
become clinically relevant entities in line with those occurring more frequently in
salivary glands (42).
Pleomorphic adenoma of the breast occurs rarely, but it closely resembles its
counterparts in salivary glands and skin, where it is also known as chondroid syringoma.
Other authors consider pleomorphic adenomas of breast to be variants of
intraductal papilloma with myxomatous osteocartilaginous stromal metaplasia (33).
Recognition of pleomorphic adenoma in breast is important because it can be over
diagnosed as malignant and result in inappropriate surgery. Indeed, Chen (34) recently
reported two new cases and reviewed 24 previously reported ones. He found that
inappropriate mastectomy was performed in 42% of cases of pleomorphic adenoma of
the breast. Appropriate therapy is local excision with a rim of uninvolved breast.
Pleomorphic adenomas of breast show little tendency to recur and even lesser
tendency to metastasize.
The clinicopathologic features of pleomorphic adenomas of the breast have been
nicely reviewed by Ballance et al. (37). Patients developing pleomorphic adenomas of
breast have ranged from 19 - 78 years, with most tumors ranging from 0.8 - 4.5 cm
(mean, 2 cm). Yet, one pleomorphic adenoma that was present for 30 years grew to 17
cm. Although pleomorphic adenomas can occur anywhere within the breast, they have
a predilection to develop near the areola. Most are well-circumscribed, but can show
multifocal growth or satellite lesions. Histologically, pleomorphic adenomas are
composed of two cell types: duct epithelial cells and myoepithelial cells. The
epithelial cells produce hyperplastic nests with focal duct differentiation (squamous
metaplasia can also occur) that merges and displays varying degrees of
osteocartilaginous metaplasia. Cytologic atypia, mitotic activity, and invasive
growth pattern are minimal. Surrounding breast tissue can appear relatively normal or
show features of proliferative fibrocystic change, including intraductal papillomas, or
non-continuous invasive carcinoma. The histologic and immunohistochemical features
suggest that pleomorphic adenomas arise from a single cell type capable of divergent
differentiation (38). That is, cytokeratin, vimentin, glial fibrillary acidic protein,
muscle-specific actin, S100 protein, epithelial membrane antigen, and GCDFP-15
expression are all variably conserved within the bimorphic population of cells found
in pleomorphic adenomas (37). Pleomorphic adenoma of breast may be over
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