January 2019
R-N14 (NP)

Signalment (JPC# 2830560):  A 12-year-old spayed female greyhound

HISTORY:  This dog had a mass in the mammary gland area.

HISTOPATHOLOGIC DESCRIPTION:  Mammary gland:  Expanding and effacing the mammary gland is a 1 x 2 cm, unencapsulated, infiltrative, multilobulated neoplasm with multifocal areas of necrosis, hemorrhage, mineralization, and acicular (cholesterol) clefts.  The neoplasm incorporates and compresses adjacent ducts and elevates the overlying epidermis.  Lobules are separated by variably thick bands of collagen and are composed of polygonal to fusiform cells arranged in islands and solidly cellular areas supported by fine fibrovascular stroma.  Neoplastic cells have variably distinct cell borders and abundant eosinophilic vacuolated cytoplasm.  Larger vacuoles (up to 50 um in diameter) peripheralize the nucleus.  Nuclei are vesiculate with one prominent magenta nucleolus.  Mitoses average 5 per 10 HPF.  There is moderate anisokaryosis and anisocytosis.  Focally, cyst-like spaces are lined by attenuated to cuboidal neoplastic cells and contain homogenous eosinophilic material and cellular debris.  Multifocally, there is scattered single cell necrosis, mineral, and small foci of cartilaginous metaplasia with neoplastic cells in lacunae.  In the surrounding tissue, there are low numbers of lymphocytes and plasma cells.  There is mild epidermal orthokeratotic hyperkeratosis.

MORPHOLOGIC DIAGNOSIS:  Mammary gland:  Malignant myoepithelioma, greyhound, canine.

SYNONYM:  Spindle cell carcinoma






Malignant myoepithelioma:


Spindle cells in short bundles surrounded by myxoid matrix

Similar basic features as malignant counterpart but minimal anisocytosis and anisokaryosis and low mitotic index



Benign mammary tumors:

Malignant mammary tumors:



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