Squamous cell carcinoma is one of the most common skin cancers in dogs, and is most commonly found in dogs around 8 years of age. Thought to be caused by exposure to ultraviolet radiation from the sun, squamous cell carcinoma occurs in both cutaneous lesions, which are found on the skin, and subungual lesions, which are found underneath the toenails. These tumors are considered invasive, but they generally do not metastasize until later in their development. Although any cancer diagnosis can be frightening, early, aggressive treatment can lead to a good prognosis.
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Frequency
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Standard poodles are prone to both types of lesions. Cutaneous lesions are more common in older dogs, especially bloodhounds, basset hounds and standard poodles. These lesions most commonly affect the head, ears, feet and abdomen, although they can also be found on the abdomen of light-colored dogs such as dalmatians and beagles because of the sparse hair coverage in that area. Subungual lesions are most common in darker-colored dogs, especially schnauzers, Kerry blue terriers and standard poodles, with the females being especially prone.
Diagnosis
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Squamous cell carcinoma is diagnosed through a combination of clinical findings and biopsy. Cutaneous lesions appear as raised, irregular sores that may be ulcerated, while subungual lesions can show itself as lameness or the loss of the toenail. If the physical exam raises suspicions of skin cancer, a small sample of the lesion will be taken for microscopic analysis of the cells.
Treatment
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Surgical removal of the tumor is necessary to stop the spread of malignant cells, and the site may also be treated with radiation. If the malignancy is advanced, chemotherapy can help stop the growth of neoplastic cells that may have spread to vital organs. If the tumor is structured in a way that makes complete removal of all margins impossible, treatment with piroxicam has been found to be an effective short-term treatment in some dogs.
Prognosis
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The prognosis for squamous cell carcinoma is good if the tumor is caught in its early stages of development, especially when surgery is followed with radiation therapy. Tumors on the nose have a slightly less favorable outcome because of the limited space for complete surgical removal but will still respond to radiation. Affected extremities such as the ear and tail can be amputated, which according to the Merck Veterinary Manual leads to a 95 percent one-year survival rate.
Prevention
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Some dogs do not mind wearing clothing to shield them from the ultraviolet rays. Limiting the dog's exposure to sunlight can help prevent a tumor from developing, but because ultraviolet rays can penetrate windows, this is not always possible. Hairless breeds and light-colored dogs with sparse coats can benefit from a liberal application of nontoxic sunblock during periods of prolonged sun exposure, and some dogs will tolerate light clothing, such as a T-shirt, to help block the sun's rays. Any skin lesions that may arise should be examined by a veterinarian, as early treatment yields the best outcome.
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