Case 4 - 170707

Eleven-year-old, male castrated dog (Shar pei)

The patient was presented to an emergency service for trouble breathing and swallowing. Examination revealed a 5 x 3 x 3 cm, pendunculated mass that appeared to arise from the soft palate. A CT of the skull revealed the mass to be ventral to the soft palate and obstructing the larynx.

One mulitlobulated, heart-shaped, soft to firm, mottled pale tan to red to purple mucosal mass measuring 4 x 4 x 1.5 cm was received.

Seven sections of similarly affected oral mucosa are examined, most of which have a bulging surface and stretched, attenuated and segmentally ulcerated overlying epithelium. The submucosa is replaced by a cell dense, poorly demarcated, unencapsulated, neoplasm that extends to deep and lateral sectional borders. The cells are highly and regionally variable, and alternately form stream, nests, and in one region sheets of round to spindloid cells with scant supportive fibrous stroma. The vast majority of the neoplastic cells have indistinct cell borders, a scant to moderate amount of eosinophilic cytoplasm, a round to elongate nucleus with finely stippled chromatin, and one to three distinct nucleoli. Anisocytosis and anisokaryosis are moderate, and there are 36 mitotic figures per ten 400x fields. Neoplastic cells frequently surround vessels. Multifocally, regions of neoplastic cells with round, hyerpchromatic nuclei with scant, eosinophilic cytoplasm form a cribiform rete with anastomosing channels of clear space. In a single region a dense sheet of cells are epithelioid. The remnant superficial submucosa is expanded by clear space (edema), large numbers of lymphocytes, plasma cells, plump, reactive fibroblasts, and extravasated erythrocytes (hemorrhage). Vessels within the submucosa are lined by plump, reactive endothelium. Small numbers of pigment-laden macrophages are scattered throughout the neoplasm. Where the surface is ulcerated, there is a fibrinoid plug with scattered embedded clusters of bacteria toward the surface.

Neoplastic cells were not immunoreactive with CD-31 immunohistochemistry. Neoplastic cells exhibited variably strong cytoplasmic immunoreactivity with PNL-2 immunohistochemistry. Neoplastic cells exhibit strong nuclear immunoreactivity with SOX-10.

Oral mass: malignant amelanotic melanoma (incompletely excised)

Immunohistochemistry revealed the mass to be a malignant melanoma. No junctional activity was noted in the sections examined, which is unusual, but the combination of antibodies characterize this as a melanoma, and definitively rule out other tumors. The histologic appearance of melanomas often varies greatly even within a single tumor as was seen in this case.

Jubb, K. V. F., Peter C. Kennedy, and Nigel Palmer. Pathology of domestic animals. St. Louis, MO: Elsevier, 2016. Print.