JPC SYSTEMIC PATHOLOGY
DIGESTIVE SYSTEM
September 2021
D-N12
Signalment (JPC #4035521): 8-month-old female Balb/c mouse
HISTORY: The mouse was culled during routine surveillance. It had a 3cm diameter, cystic, subcutaneous mass of the ventral neck and cranial chest composed of pale, friable tissue with a rich blood supply. The mass had a central cavity containing blood and viscous material. There were no other gross abnormalities.
HISTOPATHOLOGIC DESCRIPTION: Haired skin: Expanding the subcutis, elevating the overlying dermis and epidermis, and compressing atrophic pre-existing mucinous and mixed salivary glands, is a 1.25 x 1.0cm expansile, well-demarcated, partially encapsulated, moderately cellular, multilobular, multicystic neoplasm composed of spindle cells arranged in short streams and nests forming papillomatous projections, lobules, and palisading along a moderate fibrovascular stroma. Neoplastic cells have indistinct cell borders, a moderate amount of finely vacuolated basophilic cytoplasm, and oval to elongate nuclei with finely clumped chromatin and 1-2 small basophilic nuclei. Mitoses average 1-2 per 400X high power field. Multifocal neoplastic lobules contain large central areas with loss of differential staining and cellular architecture (lytic necrosis). At one margin of the section, there is a focally extensive region of mature granulation tissue within the previously described neoplasm. The neoplasm is unilaterally bordered by a focally extensive region of granulation tissue admixed with granulomatous inflammation admixed with hemorrhage and hemosiderin-laden macrophages.
MORPHOLOGIC DIAGNOSES: Haired skin, mixed and mucinous salivary glands: Myoepithelioma, Balb/c mouse, rodent.
CONDITION: Myoepithelioma
GENERAL DISCUSSION:
- Myoepitheliomas arise infrequently in most strains of mice, but are relatively common in some strains (BALB/c, BALB/cBy), especially females
- In mice, myoepitheliomas arise most frequently from submaxillary and parotid salivary glands, but may also be associated with mammary, preputial, and Harderian glands
PATHOGENESIS:
- Metastasis to the lungs may occur with large tumors
- There is frequent concomitant bone marrow and splenic myeloid hyperplasia apparently related to a secretory product of the tumor
TYPICAL CLINICAL FINDINGS:
- Most animals with salivary gland neoplasia present due to the development of a mass
- Other symptoms include halitosis, weight loss, anorexia, dysphagia, exophthalmos, Horner’s syndrome, sneezing, and dysphonia
TYPICAL GROSS FINDINGS:
- Myoepitheliomas can become very large with cystic chambers containing mucinoid fluid
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Tumors are composed of large, pleomorphic, spindle cells with epithelial and mesenchymal features lining a cystic center
- Cystic areas due to necrosis
ADDITIONAL DIAGNOSTICS:
- Immunohistochemistry:
- Myoepithelioma are reactive with AE1/AE3, CK7, CK14, p63, GFAP, and S100, while showing more variable reactivity with smooth muscle actin, actin-HHF-35, SMMHC, and calponin
- A panel that includes AE1/AE3, p63, S100, and/or smooth muscle actin will help yield the best sensitivity and specificity; in general, it is unwise to rely on a single marker
- Many antibodies highlight myoepithelial cells, including AE1/AE3, CD10, S100, GFAP, pg63, calponin, smooth muscle actin, and smooth muscle myosin heavy chain (SMMHC), all showing different sensitives and specificities
DIFFERENTIAL DIAGNOSIS:
- Salivary gland neoplasms:
- Epithelial: pleomorphic adenoma (benign mixed tumor), oncocytoma, adenocarcinoma (see D-N11), malignant mixed tumor, cystadenocarcinoma, myoepithelial carcinoma, epithelial-myoepithelial carcinoma (Park, J Comp Pathol. 2018), squamous cell carcinoma, salivary duct carcinoma, basal cell adenocarcinoma
- Non-epithelial: rare reports of osteosarcoma, infiltrative angiolipoma, melanoma, and metastatic neoplasms of other origins
- Non-neoplastic salivary gland masses: salivary gland cyst (pseudocyst AKA sialocele, true salivary cyst), salivary gland infarction (AKA necrotizing sialometaplasia, see D-M12), lipomatosis (rare, unilateral, slowly progressive enlargement of salivary gland by lobules of well-differentiated adipocytes)
- Sialoadenitis
COMPARATIVE PATHOLOGY:
- Salivary gland neoplasms are rare in all species; reported in cattle, sheep, goats, horses, dogs, cats, and rats but not swine; almost exclusively carcinomas (see D-N11); other rare neoplasms include epithelial (myoepithelioma, squamous cell carcinoma, cystadenocarcinoma) and mesenchymal (angiolipoma, fibrous histiocytoma, osteosarcoma, fibrosarcoma) malignancies that arise in salivary glands
- Rats: One case report of malignant myoepithelioma arising in the parotid gland (Schaudien, J Comp Pathol. 2020)
- Myoepitheliomas are generally considered rare in domestic animals and man; myoepitheliomas of non-salivary glands include:
- Mammary myoepitheliomas (see R-N14) are described in dogs; rare, benign neoplasms composed of spindloid cells in short bundles on a myxoid matrix; also malignant variants (i.e. malignant myoepithelioma); mammary neoplasms are common in dogs, relatively uncommon in cats, and rare in other domestic species
References:
- Barthold SW, Griffey SM, Percy DH. Pathology of Laboratory Rodents and Rabbits. 4th ed. Ames, IA: Blackwell Publishing; 2016:114-115.
- Thompson, LDR. Immunohistochemistry of head and neck lesions. In: Dabbs DJ, ed. Diagnostic Immunohistochemistry. 5th ed. Philadephia, PA: Elsevier; 2019:313.
- Foster RA. Female reproductive system and mammae. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier; 2017:1174, 1178, 1191-3.
- Gelberg HB. Alimentary system and the Peritoneum, Omentum, Mesentery, and Peritoneal Cavity. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier; 2017:353.
- Goldschmidt M, Pena L, Rasotto R, Zappulli V. Classification and grading of canine mammary tumors. Pathol. 2011;48(1):117-131.
- Munday JS, Lohr CV, Kiupel M. Tumors of the alimentary tract. In: Meuten DJ, ed. Tumors in Domestic Animals. 5th ed. Ames, IA: John Wiley & Sons, Inc.; 2017:544-9.
- Park CH, Shiwa N, Sumimoto J, Kimitsuki K. Epithelial-Myoepithelial Carcinoma in a Canine Salivary Gland. J Comp Pathol. 2018;165:52-56.
- Schaudien D, Creutzenberg O, Wagner A, Dahlmann F, Rittinghausen S. Malignant Myoepithelioma of the Parotid Gland in a Rat. J Comp Pathol. 2020;176:162-164.
- Schlafer DH, Foster RA. Female genital system. In: Maxie MG, ed. Jubb, Kennedy and Palmer’s Pathology of Domestic Animals. Vol 3. 6th ed. Philadelphia, PA: Elsevier Saunders; 2016:430-461.
- Uzal FA, Plattner BL, Hostetter JM. Alimentary system. In: Maxie MG, ed. Jubb, Kennedy and Palmer’s Pathology of Domestic Animals. Vol 2. 6th ed. Philadelphia, PA: Elsevier Saunders; 2016:30.