JPC SYSTEMIC PATHOLOGY
Signalment (JPC #3049000): An 8-year-old female spayed Belgian shepherd
HISTORY: Tissue from the right-side, fourth and fifth mammary glands
HISTOPATHOLOGIC DESCRIPTION: Mammary gland: Expanding the subcutis, infiltrating surrounding adipose and mammary tissue, and extending to a submitted margin, is an unencapsulated multilobulated neoplasm composed of polygonal cells arranged in islands and trabeculae on a fine to moderate fibrovascular stroma. Neoplastic cells have distinct cells borders with moderate to abundant eosinophilic cytoplasm containing numerous small vacuoles or a single large discrete vacuole (lipid) that frequently peripheralize the nucleus. Nuclei are round to oval with coarsely stippled chromatin and 1 variably distinct nucleolus, or are flattened and hyperchromatic. Anisocytosis and anisokaryosis are moderate. Mitoses average less than 1 per 10 HPF. Islands of neoplastic cells are separated and surrounded by thick bands of fibrous connective tissue. Multifocally, neoplastic cells are within blood and lymphatic vessels. Scattered throughout the neoplasm are aggregates of lymphocytes, plasma cells, and fewer neutrophils, occasionally admixed with necrotic debris and areas of hemorrhage with few hemosiderin-laden macrophages.
MORPHOLOGIC DIAGNOSIS: Mammary gland, right fourth and fifth mammae (per contributor): Lipid-rich carcinoma, Belgian shepherd, canine.
- Lipid-rich carcinoma is a rare neoplasm of the mammary gland in dogs, with one report of this neoplasm in a cat and one report in a Djungarian hamster
- Definitive diagnosis requires demonstration of lipid droplets in tumor cells with special stains (e.g. Oil Red O stain) or by electron microscopy
- May be found in younger intact bitches
- Often recur locally following surgical removal
- Can metastasize to local lymph nodes, bone marrow, lungs, endometrium, and the adrenal medulla
TYPICAL GROSS FINDINGS:
- Single or multiple, well-circumscribed, yellow to grey, variably sized mass or masses
- Within neoplasm, there are small areas of hemorrhage and necrosis
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Solid nest and cords of atypical round to polygonal cells with distinct cell borders
- Moderate amount of cytoplasm with numerous small intracytoplasmic vacuoles or a single large vacuole
- Nuclei are round to oval, vesicular, with clumped chromatin and 1-2 nucleoli
- Anisocytosis and anisokaryosis are moderate to marked
- Variable mitotic rate
- Lymph node metastasis and lymphatic invasion are common
ADDITIONAL DIAGNOSTIC TESTS:
- Oil-Red-O or Sudan IV to demonstrate lipid droplets
- Cytokeratin – positive; CAM 5.2 – positive; Vimentin – negative; to differentiate from liposarcoma
- Positive expression for HMW and LMW cytokeratin
- Negative expression for estrogen and progesterone receptors
- Liposarcoma: (cytokeratin negative, CAM 5.2 negative, vimentin positive)
- Location and neoplastic cells with intracytoplasmic lipid vacuoles that stain for Oil-Red-O or Sudan IV make this neoplasm unique
- Special types of mammary gland carcinoma:
- Spindle cell carcinoma: Rare in dogs, composed of spindle cells (stains +for cytokeratin), that form solid cellular areas that may contain tubules
- Squamous cell carcinoma: Solid sheets and cords of cells with areas of squamous differentiation
- Mucinous carcinoma: Rare in dog and cat, may be simple or complex type with abundant mucin production
- Lipid-rich carcinoma: Rare in dogs, cells with abundant vacuolated cytoplasm that contains large amounts of neutral lipid
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- Schlafer DH, Foster RA. Female genital system. In: Maxie MG, ed. Pathology of Domestic Animals. 6th Vol. 3. St. Louis, MO: Elsevier; 2016:460-463.
- Yoshimura H, Kimura-Tsukada N, Ono Y, et al. Characterization of spontaneous mammary tumors in domestic Djungarian hamsters (Phodopus sungorus). Vet Pathol. 2015;52(6):1227-1234.