Tumors, commonly called masses, cancers or neoplasms, are composed of new, abnormally fast-growing tissue that serves no useful purpose for the affected animal. Tumors of the skin (cutaneous) and subcutaneous soft tissue (between the outer layers of skin and the inner layers of muscle or bone) are visible lumps or bumps often seen or felt by owners. Skin tumors are the most frequently diagnosed form of cancer in companion cats.
How Skin Tumors Affect Cats
The effect of skin tumors on cats depends on the type of tumor, its size and location and its degree of aggressiveness. Normally, either the owner notices the tumor or it is discovered incidentally during a routine veterinary examination. Sometimes, skin tumors cause pruritis (itchiness), pain and/or self-trauma from scratching. Depending on their location, skin tumors can interfere with vision, smell or eating. They also can affect ambulation when located on the toes, paws or pads.
Causes of Feline Skin Tumors
The skin and underlying subcutaneous tissues are structurally complex and involve various layers and networks of skin, fibrous connective tissue, blood vessels, fat and nerves. Tumors of these areas are diverse and difficult to classify.
Neoplasms are caused by the progressive and uncontrolled growth of cells and tissue. In most cases, the precise cause of skin tumors is not known. Sometimes, they may be induced by trauma, viral infection, irritation, vaccinations and/or exposure to ultraviolet radiation. Certainly, hormones and genetics may also contribute to the development of skin masses.
Preventing Skin Tumors
Cats at risk for and previously affected by squamous cell carcinoma should be kept out of direct sunlight as much as possible. Discuss the possibility of vaccine-induced fibrosarcomas with your veterinarian. Most types of tumors cannot really be "prevented," since their cause is unknown.
The prognosis for cats with skin tumors depends entirely upon the tumor type, size, location, aggressiveness and degree of differentiation. Cats with basal cell tumors have a good prognosis, as the tumors are usually solitary and benign, and when malignant are of low-grade and rarely metastasize. Cats with multicentric fibrosarcoma caused by the feline sarcoma virus have a poor prognosis, because surgical removal typically is not possible.
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.
A number of skin tumors can occur in cats, and most owners will find unexplained lumps and bumps on their pet at some point during its life. While skin tumors can be harmless, sometimes they are malignant or proliferative and invasive and deserve prompt medical attention. A veterinarian is the best person to assess skin tumors and determine if a given bump is a benign pimple, cyst, skin tag or abscess, or if instead it is cancerous and much more serious. One of the most common initial procedures used to assess skin tumors is a fine needle aspirate. During this procedure, the veterinarian will gently insert a needle into the lump, pull back on the syringe stopper to draw out some of the fluid and cells inside the mass and then "squirt" the sample onto glass slides for microscopic examination. Other diagnostic procedures may be required as well.
Once the cause of a skin tumor has been diagnosed, the treatment options will depend on the type of tumor, its location and size, the cat's clinical signs and the tumor's degree of aggressiveness. There are several basic treatment options for skin tumors: waiting and watching; surgical excision; Laser ablation and/or cryotherapy (freezing of the affected tissue). Chemotherapy and radiation therapy may be included in the treatment protocol.
Uncomplicated benign skin tumors usually are easily identifiable microscopically using the fine needle aspirate diagnostic procedure described above. Often, these tumors do not require treatment, but they can be surgically removed for cosmetic reasons or if they seem to bother the cat. Many owners decide to have benign skin tumors removed because they do not like how they look or feel. The "wait and see" approach (called "clinical neglect") is often recommended for cats with histiocytic mast cell tumors, which typically are benign and tend to resolve without treatment. However, most skin tumors in cats are aggressive or invasive and require prompt treatment.
Skin masses that are diagnosed as malignant (or are prone to becoming metastatic) are normally removed at the first opportunity. Aggressive surgical resection, with wide margins around the tumor site, is the treatment of choice for virtually all of these skin tumors. Some feline skin tumors, such as basal cell carcinomas, can be removed fairly easily because they normally do not spread outside their margins. More aggressive skin tumors, such as fibrosarcomas, may require lengthy surgical procedures which include the removal of a margin of healthy surrounding tissue. Amputation may be recommended for animals with affected limbs.
The removed tissue will be submitted for examination by a veterinary pathologist, so that the attending veterinarian can assess whether all of the tumor cells associated with the mass have successfully been removed. If it appears that malignant cells extend close to the surgical margins, a second surgery may be necessary. Radiographs (x-rays) may be recommended to determine whether malignant forms of cancer have spread to nearby lymph nodes or other areas, particularly the bone marrow and lungs. Blood tests may be recommended as well. In many cases, radiation, chemotherapy, laser ablation and/or cryotherapy will be used in addition to surgical resection to improve the success rate. Owners must recognize that malignant tumors can recur post-operatively, despite heroic efforts by the veterinary team. Regular rechecks are important.