Transmission or Cause: Squamous cell carcinomas are common malignant neoplasms of the dog
and cat, arising from keratinocytes (skin cells). An underlying
cause is not always apparent. These tumors are most frequently
diagnosed in animals that have sun-damaged skin. Squamous cell
carcinoma is observed most frequently in geographic areas characterized
by long periods of intense sun exposure. Rarely, squamous cell
carcinoma has been reported to arise from burn scars, chronic
infectious processes, and chronic discoid lupus lesions (dogs).
Papillomaviruses of both dogs and cats can predispose an animal
to squamous cell carcinoma.
Affected Animals: In dogs, squamous cell carcinoma occurs at an average age of 9 yrs,
with no sex predilection. In general, Scottish terriers, Pekingese,
Boxers. Poodles, and Norwegian Elkhounds are predisposed. Squamous cell
carcinomas with claw bed origin are seen most commonly in black-coated
dogs of large breeds, especially Labrador retrievers, standard poodles,
giant schnauzers, dachshunds, and Bouvier de Flanders. Short-coated
breeds with white or piebald ventral coat and skin color (Dalmatian,
American Staffordshire Terrier, Bull Terrier, and Beagle) have the highest
incidence of solar-induced squamous cell carcinoma. In cats, squamous
cell carcinoma occurs at an average age of 9 yrs, with no breed or sex
predilection. White cats have squamous cell carcinoma about 13 times
as frequently as do other cats, owing to increased susceptibility to
sun damage.
Clinical
Signs: In dogs, lesions occur most commonly on the trunk, the
legs, the digits (toe), the scrotum, the lips, the anus, and the nose.
The lesions are typically ulcerated or cauliflower-like in appearance,
bleed easily and are typically solitary. Sun-bathing dogs or the claw
beds of large, black-coated breeds are more prone to multiple lesions.
Squamous cell carcinoma is the most common tumor of the digits of dogs.
In cats, lesions are most commonly observed at the external nares (nasal
openings), the ear pinnae, the eyelids, and the lips. The lesions are
typically ulcerated or cauliflower-like in appearance. About 45% of affected
cats will have multiple lesions. Generally, squamous cell carcinomas are
locally invasive and slow to spread. In both dogs and cats, squamous cell
carcinomas arising from the digits appear to be more aggressive.
Diagnosis: The diagnosis is typically made with a skin biopsy. Other diseases that
need to be considered include other forms of cancer as well as infectious
diseases (bacterial, fungal). Clawbed lesions are frequently misdiagnosed
as infectious in nature.
Prognosis: Squamous cell carcinomas are generally locally invasive but are slow to
spread. Spread to regional lymph nodes and lungs is seen with advanced
neoplasms. Tumors of the claw bed are more aggressive and can invade underlying
bone as well as spread to regional lymph nodes more often compared to
other locations. Squamous cell carcinoma of the digits of cats is the
most aggressive of the locations and carries the poorest of prognoses
as it spreads quickly (slower spread in dogs).
Treatment: Clinical management of squamous cell carcinoma may include surgical excision,
cryotherapy (freeze/thaw), electrosurgery, hyperthermia, radiotherapy,
and chemotherapy. Avoidance of sunlight is an important part of prevention.
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