JPC SYSTEMIC PATHOLOGY
Signalment (JPC #2147437): Dog
HISTOPATHOLOGIC DESCRIPTION: Haired skin: Expanding the deep dermis and subcutis, elevating the overlying dermis and epidermis, and extending to one cut border is a multilobulated, unencapsulated, well circumscribed, densely cellular neoplasm composed of polygonal cells arranged in haphazard ductules and islands separated by variably thick bands of fibrous connective tissue. Ductules often have slit-like lumens lined by double layers of epithelial cells. The luminal layer is composed of cuboidal cells that have variably distinct cell borders, scant to moderate amounts of eosinophilic granular cytoplasm, oval nuclei with finely stippled chromatin and generally one distinct nucleolus. Cells on the abluminal layers are more flattened and often oriented parallel to the basal lamina. There is mild anisocytosis, anisokaryosis, and mitotic figures average 1 per 40x HPF. Tubules are often distended up to 1.5 mm diameter with brown to amphophilic granular secretory product with clear, acicular cholesterol clefts. Multifocally, there is squamous differentiation of tubular epithelium with intraluminal lamellations of keratin which primarily exhibit gradual keratinization characterized by the presence of keratohyalin granules. Scattered within the fibrous connective tissue and within tubules are moderate numbers of secretory product-laden macrophages.
MORPHOLOGIC DIAGNOSIS: Haired skin and subcutis: Apocrine ductular adenoma, breed unspecified, canine.
CONDITION: Apocrine ductular adenoma; epitrichial ductular adenoma
SYNONYMS: Basaloid apocrine adenoma
- An uncommon benign apocrine sweat gland neoplasm of the deep dermis and subcutis in older dogs and cats with differentiation to apocrine ductal epithelium
- Most commonly found on the head, thorax, abdomen, and back in dogs and primarily on the head in cats
- Some authors recognize two types:
- Classical apocrine ductular adenoma- more common in dogs, but reported in cats as well
- Solid-cystic apocrine ductular adenoma- a subtype previously classified as basal cell tumor, more common in cats; may be locally aggressive but rarely metastasize
- Old English sheepdog, golden retriever, and English springer spaniel may be predisposed
TYPICAL GROSS FINDINGS:
- A solitary, slow growing, > 2cm diameter, well-demarcated, firm, raised, multilobulated and occasionally cystic, intradermal or subcutaneous mass
- Overlying skin often thin and alopecic, but usually not ulcerated
- Often has a blue or purplish tint when viewed through overlying skin
- Greyish or gelatinous material in cystic spaces
- Solid-cystic apocrine ductular adenomas may be pigmented; most common on the head, neck and dorsal trunk of cats
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Hallmark features: A circumscribed, unencapsulated, multilobular neoplasm characterized by a proliferation of a double layer of epithelial cells lining a slit-like lumen or forming tubules (ducts)
- There may be central cystic degeneration
- Luminal, cuboidal cells have scant clear cytoplasm, small hyperchromatic nucleus. Outer layer cells are more fusiform with euchromatic nuclei
- There is little cellular or nuclear pleomorphism and moderate mitotic activity
- Dogs: Gradual keratinization, squamous metaplasia, irregular keratin lakes
- Neoplasm is not contiguous with the epidermis
- Solid-cystic apocrine ductular adenoma - cats
- Multilobulated or racemiform (grape-like) with islands, solid sheets or cysts lined by undifferentiated basaloid cells; focal epidermal contiguity often present; oriented vertically within the dermis
- Central cystic degeneration and necrosis of tumor lobules often with central necrosis and melanin pigment within tumor cells and macrophages
- Two distinct polygonal cell morphologies: (1) Small, cuboidal, basaloid appearance, concentrated around periphery without palisading, comprise majority of trabecular structure with occasional ductules, (2) larger polygonal cells with rounded margins in center of islands, intracytoplasmic vacuoles with smooth borders consistent with intracellular ductal differentiation; spindling may be present in either population
ADDITIONAL DIAGNOSTIC TESTS:
- Cytokeratin positive; CK7/8 (CAM 5.2) and CK13 are relatively specific markers for glandular epithelia
- Basaloid (ductular) mammary gland adenoma: Virtually identical except for identifiable mammary glands
- Ductular adenocarcinoma: Irregular, infiltrative borders; tubules lined by double layer of pleomorphic neoplastic cells with larger nuclei, prominent nucleoli and atypical mitotic figures; ulceration and necrosis are common but metastasis is not
- Ribbon trichoblastoma: Lacks double layered tubules and gradual keratinization
- Trichoepithelioma: Lack tubules or lobules; exhibits basaloid and squamous populations, true keratin cysts and usually more superficial
- Cats: Classic apocrine ductular adenoma is a well-circumscribed, small lobular neoplasm with sheets of uniform basal cells and double-layered tubules with cyst-like structures; usually in deep dermis without epidermal contiguity; low mitotic activity; melanization is rare (in contrast to solid-cystic apocrine ductular adenoma)
- Must differentiate from apocrine cystadenomas and solid-cystic apocrine ductular adenomas
- Horses: Rare; most commonly found on the pinna and vulva; one case of multiple apocrine gland ductal carcinomas in all four limbs
- Cihocki LM, Divers TJ, Johnson AL, Warren AL, Schramme M, Rassnick KM, Scott DW. A case of multiple epitrichial sweat gland ductal carcinomas in a horse. Vet Dermatol. 2007;18(2):134-137.
- Goldschmidt MH, Dunstan RW, Stannard AA, von Tscharner C, Walder EJ, Yager JA. Histological Classification of Epithelial and Melanocytic Tumors of the Skin of Domestic Animals, 2nd Series, Vol. III. Washington, DC: Armed Forces Institute of Pathology; 1998: 28-32, 69-71.
- Goldschmidt MH, Hendrick MJ. Tumors of the skin and soft tissues. In: Meuten DJ, ed. Tumors in Domestic Animals, 4th ed. Ames, IA: Iowa State Press; 2002: 70-74.
- Goldschmidt MH, Shofer FS. Skin Tumors of the Dog and Cat. Oxford, England: Pergamon Press; 1992: 85-89.
- Gross TL, Ihrke PJ, Walder EJ, Affolter VK. Skin Diseases of the Dog and Cat, 2nd ed. Ames, IA: Blackwell Science; 2005: 625-634,672-674.
- Pieper JB, Stern AW, LeClerc SM, Campbell KL. Coordinate expression of cytokeratins 7 and 14, vimentin, and Bcl-2 in canine cutaneous epithelial tumors and cysts. J Vet Diagn Invest. 2015; 27(4): 497-503.
- Scott DW, Miller WH. Equine Dermatology. St. Louis, MO: WB Saunders; 2003: 717.