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Cutaneous Apocrine Gland Tumors |  |
| Sweat glands are of two types: apocrine and eccrine. Apocrine glands are tubular glands with a coiled secretory portion and a long straight duct that empty into the follicular infundibulum. In domestic animals, all hair follicles have apocrine glands. Apocrine glands in dogs and cats are also present in association with the anal sac, and modified apocrine glands, known as ceruminous glands, are present in the external auditory meatus. In most mammals, apocrine glands produce an
odiferous, oily compound that is a sexual attractant, a territorial marker, and a warning signal. In horses and cattle, these glands play a role in thermoregulation by producing sweat. |
| Apocrine gland tumors and malformations are most common in dogs and cats. Three diseases of apocrine glands of haired skin have been characterized. |
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Cystic apocrine gland dilations
(apocrine gland cysts,
cystic apocrine gland hyperplasia,
apocrine cystomatosis) are best characterized as hamartomas. Two forms exist: a cystic form in which one or more cysts develop in the mid to upper dermis with a poor association with hair follicles, and a more diffuse form characterized by cystically dilated apocrine glands associated with multiple hair follicles in nontraumatized skin. Both are found in middle-age or older dogs and, less commonly, cats. The head and neck are
the most common sites where these lesions develop. In both species, lesions appear as fluctuant dermal cysts or as translucent bullae. Complete excision is curative; however, this may be difficult to accomplish in the more diffuse form. |
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Apocrine gland adenomas are diagnosed almost exclusively in dogs, cats, and rarely horses. Two types are recognized based on whether their histologic appearance primarily resembles the secretory or ductular portion of the apocrine gland.
Apocrine adenomas resemble the secretory region of the apocrine glands. They are found in older dogs and cats. Great Pyrenees, Chow Chows, and Alaskan Malamutes are the most commonly affected breeds. The head, neck, and extremities are the most frequent sites of development. In cats, apocrine adenomas are more likely to occur in males, and no breed appears at greater risk than any other. The vast majority occur on the head, especially the pinnae. In horses, no age, sex,
or breed association is known. The pinnae and vulva are the most likely regions to develop these tumors. In all species, these tumors appear as firm to fluctuant cysts, seldom >4 cm in diameter. They contain varying amounts of clear to brownish fluid. In cats, the luminal fluid may be darkly pigmented, and apocrine cysts can be confused clinically with melanocytomas, especially when present on the inner aspect of the ears.
Apocrine ductular adenomas are less common. They are found in older dogs and cats and are putatively derived from or show differentiation toward apocrine ducts. In dogs, these tumors are most commonly recognized in Peekapoos, Old English Sheepdogs, and English Springer Spaniels. They are often smaller, firmer, and less cystic than apocrine adenomas. Because they often consist of a large population of basal cells and because evidence of ductular differentiation can be
extremely subtle, these tumors are often diagnosed histologically as basal cell tumors (see
Basal Cell Tumors and Basal Cell Carcinomas). Apocrine adenomas and apocrine ductular adenomas are benign, and complete surgical excision is curative. |
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Apocrine gland adenocarcinomas of haired skin are rare in all domestic animals but most frequently identified in older dogs and cats. In dogs, Treeing Walker Coonhounds, Norwegian Elkhounds, German Shepherds, and mixed-breed dogs are most at risk; in cats, Siamese may be predisposed. In both species, this tumor most commonly arises in axillary and inguinal regions—sites that allow it to be easily confused
clinically and histologically with mammary gland ductular adenocarcinomas. Apocrine gland adenocarcinomas generally are larger than adenomas and have a variable clinical appearance ranging from fibrotic dermal nodules to ulcerated plaques. They are locally invasive and frequently metastasize to draining lymph nodes. Less commonly, skin and lung metastasis may occur. Complete surgical excision is the treatment of choice. Little is known about response to adjunct chemotherapy. |
