Page 1417 - Clinical Small Animal Internal Medicine

154 Nonmelanoma Skin Cancers 1355

Trichoepitheliomas are tumors that demonstrate growing or static in growth pattern, and may be alopecic,
VetBooks.ir differentiation into elements of the hair follicle, and are ulcerated, and of blue‐black or pink color. Cysts and seba­
seen on the limbs, neck, and back of bassett hounds,
ceous adenoma lesions may rupture or become infected,
coonhounds, setters, and English springer spaniels.
ers assume that squamous cell carcinoma on the nose of
These are rarely malignant, and are referred to as and thus may wax and wane in size. In many cases, own­
malignant trichoepitheliomas or metrical carcinomas a cat is a result of an infected fight wound. In these cases,
in those rare cases. there is a wound that fails to heal properly, and is inter­
Pilomatricomas are tumors of hair matrix cells, and are mittently scabbed or open and bleeding. Similarly, der­
also benign in general. Kerry blue, soft‐coated wheaten, mal hemangiosarcomas arise in areas of actinic injury,
and Airedale terriers are the most affected, as are with a clinical appearance of small red spots or “blood
standard poodles, bichon frise, old English sheepdogs, blister” lesions that may bleed or become invasive.
and bouviers des Flandres. These lesions may ulcerate
and ossify. While these lesions are rarely malignant, they
are reported to be highly metastatic when malignant Diagnosis
transformation occurs.
Neuroendocrine tumors of the skin are referred to as Diagnosis of skin tumors is by cytology or biopsy.
Merkel cell tumors. They are thought to arise from Because these patients are often older, a minimum
mechanoreceptors in the skin, and are also rare in dogs database (complete blood count, serum chemistry
and cats. While these tend to be highly malignant in panel, and urinalysis) is helpful in anesthetic planning.
humans, they are more benign in dogs. However, skin tumors are not typically associated with
Ear canal tumors can be classed with skin tumors as paraneoplastic syndromes that could be detected on
a continuous cutaneous organ. Most commonly seen bloodwork. Interestingly, humans affected by squamous
are ceruminous gland adenomas and carcinomas. cell carcinoma may have hyperglobulinemia that is of
Ceruminous glands are modified apocrine glands local­ polyclonal nature and directed against specific cytokerat­
ized to the ear canal. Other tumors of the ear canal ins. Hyperglobulinemia may be noted in cats with sun­
include squamous cell carcinomas, basal cell carcino­ light‐induced squamous cell carcinoma as well, although
mas, mast cell tumors, histiocytomas, sebaceous gland it is clinically insignificant.
tumors, plasma cell tumors, melanomas, and various The method of biopsy is determined by size and
sarcomas. Benign polyps arising in the ear canal are also location of the lesion. Small superficial lesions may be
noted, particularly in young cats. best managed by excisional biopsy, which can be both
diagnostic and therapeutic. Larger lesions may require
incisional biopsy to allow for surgical or radiation treat­
Signalment ment planning. Advanced local imaging with computed
tomography (CT) or magnetic resonance imaging (MRI)
Most cutaneous tumors arise in aged animals, as it can may be helpful in determining the full extent of the lesion
take a lifetime of exposure to environmental carcino­ to be addressed.
gens, coupled with geriatric waning of immune surveil­ Carcinomas of the skin may merit clinical staging with
lance, to allow tumors to manifest. Occasionally skin lymph node aspiration cytology or lymph node biopsy
tumors will arise in younger animals, particularly in cats and thoracic radiographs. Abdominal staging may be
affected by retroviruses or feline papillomavirus. There considered in cases with malignant lesions on the cau­
is generally no sex predisposition in the development dal portion of the body, where lymphatic spread to
of skin cancer. Many specific histologic types of skin intrapelvic or intraabdominal node sites may occur.
cancer, particularly those arising in adnexal structures, Lymphadenomegaly should be investigated with cytology
are breed associated, as described in the section on or biopsy. Pulmonary metastasis is rarely seen in dogs
epidemiology. with skin cancer, although squamous cell carcinoma
(SCC), malignant pilomatricomas, sebaceous gland car­
cinomas, apocrine gland carcinomas, and neuroendocrine
History and Clinical Signs carcinomas have the potential to metastasize.
Ear canal tumors often cause pain, malodorous
In most cases, the first sign of skin tumor development is discharge, difficulty opening the mouth and neuro­
the presence of a mass. Masses may be indolent in their logic signs such as facial palsy and vestibular signs.
growth pattern or may be rapidly progressive. Skin These signs may lead to delayed diagnosis of tumor, as
tumors are generally nonpainful, unless infection or patients may undergo protracted periods of treatment of
inflammation occurs. Basal cell tumors tend to be slowly suspected otitis before biopsy diagnosis is obtained.