Page 382 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

360 PART IV Specific Malignancies in the Small Animal Patient

rare in dogs and cats, with only one report of a dog with involve-
ment of multiple pads on one foot. 143 Wide surgical excision is the
92
recommended treatment.
VetBooks.ir Neuroendocrine Carcinoma
Neuroendocrine carcinoma is also known as Merkel cell car-
cinoma. Merkel cells are thought to be part of the mechanore-
ceptor in the skin. Recent studies have demonstrated a role for
the Merkel cell polyomavirus in the development of human
Merkel cell tumors. 144 Merkel cell tumors are highly malignant
in humans; however, most case reports in cats and dogs suggest
a more benign clinical course, 141,145 although distant metastasis
has been reported in both species. 142,146,147 A recent evaluation
of two canine neuroendocrine carcinomas demonstrated expres-
sion of β-catenin or E-cadherin, proteins whose loss predicts a
more malignant behavior in humans. 148 There was also expression
of chromogranin-A, neurone-specific enolase, S-100, and c-kit • Fig. 19.4 Typical appearance of a ceruminous gland cyst in the ear of a cat.
(which is also expressed in human neuroendocrine carcinomas).
Current treatment recommendations reflect the generally benign
behavior of these tumors and consist of wide surgical excision.
The efficacy of chemotherapy for treatment of metastatic neuro-
endocrine carcinomas is unknown, as is the effect of c-kit targeted
tyrosine kinase inhibition.
Renal Cystadenocarcinoma and Nodular Dermatofibrosis
Nodular dermatofibrosis is a pathognomonic cutaneous syndrome
associated with renal cystadenocarcinomas, primarily described in
German shepherd dogs. 66,69 These dogs have multiple firm, haired
masses all over their bodies. On histopathologic examination these
nodules are composed of dense, irregular collagen. They do not
typically cause clinical problems unless they cause lameness or
otherwise disrupt normal function. Surgical removal is indicated
in these instances. Most of these dogs die as a result of renal fail-
ure or progressive renal cystadenocarcinoma (see Chapter 30), on
average 3 years after initial detection of the dermatofibrosis. 149
There are no known effective treatments for the renal cysts or
bilateral renal adenocarcinoma. A recent case report of nodular
dermatofibrosis in an Australian cattle dog without any evidence
of renal cysts or adenocarcinoma at necropsy suggests the possibil-
ity of a nonlethal version of this syndrome. 150
• Fig. 19.5 Aural ceruminous gland carcinoma confined to the vertical ear
Tumors of the Ear Canal canal in a cocker spaniel. (Courtesy Michelle Oblak.)

Ceruminous glands are modified apocrine glands found in the and pendunculated, although they can also be ulcerated. 155 Cats
external ear canal. Benign and malignant tumors arising from with ceruminous gland adenomas are slightly younger than those
these glands are the most common tumor types in the ear canal presenting with malignant tumors; in dogs both lesions present
of dogs and cats. Additional tumor types that have been reported around 9 years of age. 154,155 Cocker spaniels and poodles are pre-
include SCC, undifferentiated carcinoma, BCC, hemangiosar- disposed. Surgery is the treatment of choice.
coma (HSA), MCT, melanoma, and benign fibroma, papilloma, Ceruminous gland cysts are found in cats. These are darkly pig-
sebaceous gland tumors, ceruminous gland cysts, and histiocyto- mented, sessile masses that are usually <5 mm in diameter and can
mas. 151–154 Inflammatory polyps also are found in dogs and more occur as multiple lesions (Fig. 19.4). 153 If necessary, these can be
commonly in cats. surgically excised.
Most tumors of the ear canal are diagnosed as a result of the
mass effect, which may cause clinical signs such as chronic otitis Ceruminous Gland Adenocarcinoma
or partial deafness. Occasionally patients may present for pain on Ceruminous gland adenocarcinoma is the most common malignant
opening of the mouth or neurologic signs. This is more common tumor of the ear canal in both dogs and cats (Fig. 19.5). In dogs,
with malignant tumors. 154 The role of chronic otitis in the devel- cocker spaniels and German shepherd dogs are at increased risk .
155
opment of these tumors is an area of ongoing discussion. Malignant ceruminous gland tumors are more common than benign
tumors in cats; however, there is conflicting information on whether
Ceruminous Gland Adenoma and Cyst malignant or benign tumors are more common in the dog. 155,156
Ceruminous gland adenomas are benign tumors of the cerumi- Ceruminous gland adenocarcinomas have metastatic poten-
nous gland. On gross appearance they are typically exophytic tial, and full staging is recommended before treatment. Local