Skin tumors are among the most commonly diagnosed neoplastic disorder in domestic animals, including both cats and dogs, probably because they are so readily noticeable. The skin is the largest organ in the body, and obviously it is regularly exposed to outside environmental hazards such as ultraviolet radiation, chemical carcinogens and bacterial, fungal or viral microorganisms. A variety of skin tumors occur in cats, and older cats are particularly at risk. If you notice any unusual lump or bump on or under your cat’s skin, it is best to have it examined by a veterinarian as soon as possible. The most frequently diagnosed skin tumors in cats are basal cell carcinomas, squamous cell carcinomas, mast cell tumors and fibrosarcomas.
Basal Cell Tumors
Basal cell tumors are among the most common skin tumors diagnosed in cats – especially in older cats. Siamese, Domestic longhair, Himalayan and Persian breeds are predisposed. Basal cell tumors usually appear as solitary, round, well-defined, hairless intradermal skin masses, and they can develop almost anywhere on the cat’s body. These tumors tend to be highly pigmented and prone to ulceration. They most often are benign. When they are malignant, basal cell carcinomas tend to show up on the cat’s head, neck or legs. Complete surgical excision is the treatment of choice for basal cell tumors.
Squamous Cell Carcinoma
Squamous cell carcinoma (SCC) is thought to arise from the outer root sheath of hair follicles. SCC occurs in all domestic animals, but especially in older white cats with prolonged exposure to intense sunlight. Most commonly affected are thinly-haired, non-pigmented areas on the tips of the ears, eyelids, nose and lips. There is no reported breed or gender predisposition in cats. Feline squamous cell carcinoma manifests as proliferative, usually small, crusty and/or ulcerating facial sores that do not heal and are prone to bleed. They tend to be moderately invasive and can be malignant. Surgical excision with wide margins is recommended.
Mast Cell Tumors
Cutaneous mast cell tumors are common in cats. They occur most frequently in animals over four years of age, with the Siamese breed being predisposed. In cats, mast cell tumors usually appear as a solitary nodule just under the surface of the skin, which may be hairless and/or ulcerated. Histiocytic mast cell tumors are a form unique to cats – especially Siamese cats under the age of four. This form appears as multiple, small firm masses clustered anywhere on the body, which typically resolve spontaneously without medical attention. Unlike in dogs, mast cell tumors in cats usually are well-differentiated and considered benign. Wide surgical excision of solitary masses is recommended and often curative.
Fibrosarcomas are common superficial soft-tissue tumors in cats. They are aggressive and malignant and can vary widely in appearance, size and location. Typically, they are poorly circumscribed, nodular to irregular in shape, fleshy and firm and appear on the cat’s legs, ears and/or chest. They tend to cause bruising and typically rapidly increase in size. Three types of fibrosarcomas are recognized in cats: a multicentric form in young cats (usually less than 4 years of age) caused by the feline sarcoma virus; a solitary form in cats of any age; and a vaccine-induced form that can present at the site of vaccine injections.