Page 381 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 19 Tumors of the Skin and Subcutaneous Tissues 359

Common locations include the limbs, neck, and back, and cocker spaniels. 132,133 Coonhounds, Nordic breeds, and some ter-
multiple trichoepitheliomas have been reported in basset hounds riers may also be predisposed to benign sebaceous tumors. 134 The
limbs, trunk, and eyelids were the most common locations for
and English springer spaniels. Surgical excision is the preferred
VetBooks.ir treatment, except in cases with a multicentric presentation. 126 these benign sebaceous tumors. Although these can occur even
in young dogs, the peak occurrence is 7 to 13 years of age.
132–134
Malignant Trichoepithelioma
Sebaceous epitheliomas may recur locally, and LN metasta-
Malignant trichoepithelioma is differentiated from its benign sis has been reported anecdotally. 135 Because lymphatic invasion
variant on the basis of invasion into the surrounding tissues and occasionally may be found at the margin of sebaceous epithelio-
lymphatic involvement. It is also known as matrical carcinoma, mas, these tumors sometimes are considered a low-grade malig-
and it may be difficult to differentiate from a malignant piloma- nancy rather than a benign tumor. A recent report of distant
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trixoma. 127 The mitotic index is usually higher in malignant metastasis in a dog with a recurrent sebaceous epithelioma con-
trichoepithelioma compared with the benign counterpart. The firms their malignant potential. 135 In general, adequate surgical
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few described cases in the literature were highly metastatic to the excision is the preferred treatment.
regional LNs and lungs. 126 The locally invasive nature of some
trichoepitheliomas may also represent a lower grade variant of Sebaceous Gland Carcinoma
malignant trichoepithelioma. 127 Wide surgical excision is recom- Sebaceous gland carcinomas are uncommon in the dog and cat.
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mended. 126 No information is available on response to adjuvant They are more common in intact male dogs, and the Cavalier
therapies. King Charles spaniel, cocker spaniel, and terrier breeds are pre-
disposed. 134 The tumors typically are found on the head and neck
Pilomatricoma in dogs and on the head, thorax, and perineum in cats. Seba-
Pilomatricoma is a benign follicular tumor demonstrating only ceous carcinomas tend to be low-grade malignancies, with distant
matrical differentiation. Alternative names for this tumor metastasis reported in one dog. 136,137 The most common finding
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include the necrotizing and calcifying epithelioma of Malherbe of malignancy is local infiltration. Wide surgical excision is the
and pilomatrixoma. These tumors are uncommon, represent- recommended treatment.
ing 13% of the follicular lesions in one study and approximately
1% of all skin biopsies. 119 They are rare in the cat, with only one Apocrine Gland Adenoma and Solid-Cystic Apocrine
case described in 1225 skin biopsies. 2,6,7,15 Breed predispositions Ductal Adenoma
include the Kerry blue terrier, soft-coated wheaten terrier, Bouvier Apocrine gland adenomas are relatively common in dogs but
des Flandres, standard poodle, old English sheepdog, bichon frise, uncommon in cats. The solid-cystic apocrine ductal adenoma pre-
and Airedale terrier, among others. 92,128 The mean age at presen- viously was designated a BCT. Apocrine ductal adenomas are firm
tation is 6.5 years. 128 The most common locations are the neck, or fluid filled on palpation. Feline apocrine adenomas have a high
back, and trunk. These tumors are typically well circumscribed predilection for the head. 138 Surgical excision is the recommended
and may be very firm as a result of ossification. 127,128 Surgical exci- treatment.
sion is the recommended treatment.
Apocrine Gland Carcinoma
Malignant Pilomatricoma Apocrine sweat gland tumors are relatively uncommon in dogs
Malignant pilomatricoma is thought to be a rare tumor, although (1% of all skin tumors) and cats (3% of all skin tumors) (see Tables
a recent study suggests it may be more common than previously 19.1 and 19.2). In a series of apocrine gland tumors, 40 of 44 dogs
reported, with four malignant variants described from a total of and 8 of 10 cats had malignant apocrine gland carcinomas. 139 In
13 pilomatricomas. 129 Malignant pilomatricoma has not been dogs the median age at diagnosis is 9 years, with most tumors
reported in cats. Differentiating benign and malignant pilomatri- occurring between 6 and 11 years of age. 140 Golden retrievers and
comas can be difficult histologically. 130 Invasion into underly- the Treeing Walker coonhound may be predisposed. 138,139 The
ing tissues, particularly bone, may be an indicator of potential thoracic limbs are the most common site in dogs. Apocrine gland
malignant behavior in the absence of a malignant histologic carcinomas were diagnosed in cats ranging from 6 to 17 years of
appearance. 129–131 A recent review of several published cases dem- age, and no breed or sex predilections were identified. 138,139 The
onstrated a high metastatic potential with metastasis to the lungs, most common locations for this tumor in cats include the head,
bone, LN, mammary gland, or skin in 11 of 12 dogs. 129 There limbs, and abdomen. 138 In both species most lesions are solitary.
is one report of a dog with recurrent malignant pilomatricoma In addition to the nodular tumors, apocrine gland carcinomas
being treated with surgery and RT; this dog was diagnosed with may present as erosive and inflammatory skin disease, termed
pulmonary metastasis 14 months after local treatment. 130 The effi- “inflammatory carcinoma.” 138
cacy of chemotherapy for the treatment of dogs with malignant Local invasion is common, with 66% of tumors demonstrat-
pilomatricoma is unknown. ing invasion of the capsule and/or stroma, and 11% invading the
vasculature. 140 In another series 23% had lymphatic invasion. 139
Tumors of Glandular Origin Grossly no features differentiated benign from malignant tumors.
Despite the high incidence of local invasion, cure rates are high
Sebaceous Hyperplasia, Sebaceous Adenoma, Sebaceous with surgery alone; only two dogs developed local recurrence
Ductal Adenoma, and Sebaceous Epithelioma (4%) and one dog developed distant metastasis (2%) in two case
Tumors of glandular origin are very common in the dog but series. 139,140 Surgery is the recommended treatment.
rare in the cat, and divisions between these tumors may be arbi-
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trary. A review of 172 sebaceous gland tumors in dogs revealed Eccrine Adenoma and Carcinoma
a female predisposition for sebaceous hyperplasia and an over- Eccrine adenoma and carcinoma are benign and malignant
representation of miniature schnauzers, beagles, poodles, and tumors, respectively, of the sweat glands of the footpads. They are