Page 380 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

358 PART IV Specific Malignancies in the Small Animal Patient

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• Fig. 19.3 Large trichoblastoma on the muzzle of a dog. Local surgical excision was curative.

survival (PFS) rate at 1 year. 112 Electrochemotherapy with When surgical excision is not feasible, treatment with isotreti-
intravenous bleomycin has shown an 82% CR rate for 2 noin (1.7–3.7 mg/kg/day) proved effective in three of seven
months to 3 years in cats with cutaneous SCC; it may be a good dogs, with one CR and two PRs. 121
option for the treatment of lesions for which surgical resection
may be challenging. 113 Two dogs with metastatic SCC were Tricholemmoma
treated with cisplatin. 114 One dog with cutaneous SCC meta- Tricholemmomas are rare, benign tumors in dogs. 123,124 They are
static to the axillary LN and lungs had a marked reduction in well-encapsulated cutaneous or subcutaneous masses that may
the number and size of lung nodules, in addition to a partial cause hair loss in the overlying skin. The most common location
response (PR) of the axillary LN after cisplatin chemotherapy; appears to be the head. 119 Surgical excision is the treatment of
however, the response duration was only 4.5 months. The other choice.
dog had a complete and durable response of multiple lesions
(>22 months). Bleomycin has demonstrated short-lived clini-
cal activity in the treatment of both dogs and cats with SCC. 115 Trichoblastoma
Two dogs with SCC were treated with actinomycin-D; one dog Trichoblastoma is the new designation for what previously was
had stable disease after a single dose, and the second dog had called BCT in the dog and spindle cell variant of BCT in the
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a PR after treatment with a total of six doses. 116 Mitoxantrone cat. Histologically this tumor shows differentiation to the
resulted in a response in four of nine dogs with SCC in one hair germ of the developing hair follicle. Breeds at increased
study, but only 4 of 32 cats with SCC. 117,118 risk of developing trichoblastomas include poodles and set-
ters. 119 Trichoblastomas are common in both dogs and cats.
Tumors with Adnexal Differentiation In a review of follicular tumors and tumorlike lesions, tricho-
blastomas comprised 26% of 308 canine follicular lesions and
A number of tumors arise from the hair follicle, and most of approximately 2% of all skin biopsies, and 26% of 50 feline
them are benign. Treatment for these benign tumors is surgical follicular lesions (<2% of all skin biopsies). 119 The mean age
excision. Characteristics unique to these tumors are discussed at diagnosis was approximately 7 years for dogs and 10 years
individually. for cats. 119 The most common sites for trichoblastomas are the
head and neck in dogs and the head, neck, limbs, and trunk
in cats (Fig. 19.3). Although at least six subtypes have been
Infundibular Keratinizing Acanthoma described (ribbon, medusoid, trabecular, spindle, granular cell,
Infundibular keratinizing acanthoma (IKA) is a benign tumor. and clear cell), trichoblastomas are benign and the subtype
It is common in dogs but has not been reported in cats. Previ- does not affect the prognosis. Surgical excision is the treatment
ous names for this tumor include intracutaneous cornifying of choice. 92,125
epithelioma (ICE), intracutaneous keratinizing epithelioma,
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keratoacanthoma, and squamous papilloma. Peak incidence
is from 4 to 9 years of age, but IKAs can occur in younger Trichoepithelioma
dogs. 119 Nordic breeds (particularly Norwegian elkhounds), Trichoepithelioma is an uncommon benign tumor in cats and
Belgian sheepdogs, Lhasa apso, German shepherd dogs, ter- dogs comprising approximately 4% of follicular tumors and
riers, and other breeds appear to be at increased risk for the tumorlike lesions. 119 These tumors demonstrate differentiation
development of these tumors. 119–122 They occur most com- into all segments of the hair follicle ; they are dermal in origin
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monly on the back, neck, trunk, tail, and upper limbs, and but can extend into the subcutis. Their surface can be ulcerated or
they may appear as solitary or multiple lesions. 119–122 They alopecic. Predisposed breeds include the basset hound, bullmas-
may have a central pore that communicates with the surface. tiff, standard poodle, soft-coated wheaten terrier, English springer
Rupture of these masses can allow keratinized tissue into the spaniel, golden retriever, schnauzer, and setters. 92,119,126 Persian
adjacent dermis and incite a marked inflammatory response. cats may or may not be predisposed. 92,126