Defining Cancer in Cats
Cancer in cats, medically referred to as “neoplasia,” is defined as a malignant cellular tumor. A tumor, which is an overgrowth of abnormal cells and/or the transformation of good cells into bad cells, can be either benign or malignant. Benign (which is good and means that they are usually harmless), or malignant (which is bad and means that they are invasive and tend to spread from one part of an animal’s body to other areas, which is called “metastasis”). Malignant tumors almost always eventually cause death. Most cancers are more common in older cats and those that are not neutered or spayed, although lymphoma tends to target younger animals. Cats infected with the feline leukemia virus (FeLV) or feline immunodeficiency virus (FIV) are at an increased risk of developing cancer.
Types of Cancer in Cats
Lymphoma, also called lymphosarcoma, is an aggressive type of cancer that involves rapid division, transformation and spread of white blood cells called “lymphocytes”. It is common in cats – especially those infected with the feline leukemia virus (FeLV) or feline immunodeficiency virus (FIV). Males seem predisposed to developing lymphoma. It also is more common in house cats exposed to cigarette smoke. Lymphoma often targets the digestive tract (stomach, small intestine, large intestine, rectum), spine and tissues in the chest cavity. The lymph nodes, spleen, liver and bone marrow can also be involved. The symptoms of lymphoma depend upon which organs are affected. If diagnosed and treated early, lymphoma often can be well-managed. Many cats achieve complete remission after a course of chemotherapy. Without treatment, the prognosis is poor.
Cats usually have four pairs of mammary glands. Malignant tumors of those glands are common in older unspayed females and are the third most prevalent type of cancer in domestic cats. Siamese cats and females with calico coats are predisposed to developing breast cancer. Most mammary tumors are adenocarcinomas that start in the cat’s front mammary glands, although the back glands certainly can be affected. Approximately 90% of feline mammary masses are aggressively malignant, which means that they spread fast and far, often to the lungs and lymph nodes. As breast cancer progresses, the tumors can ulcerate and rupture, becoming quite painful. Surgical removal is the treatment of choice for all cats with breast masses, although surgery won’t cure the condition if the cancer has already spread. Chest X-rays (radiographs) should be taken before deciding whether to perform a mastectomy. Chemotherapy can be helpful in some cases. The outlook for cats with mammary cancer depends on how early it is caught and the size of the tumors when they are discovered.
Skin cancer is common in cats. Many skin tumors are benign (harmless), while others are malignant (dangerous). The most common types of feline skin cancer are basal cell carcinomas, squamous cell carcinomas, mast cell tumors, melanomas and fibrosarcomas. Skin masses can be small or large, soft or firm, above or under the skin and solitary or clustered. They can grow slowly or quickly. Many skin tumors spread if they aren’t taken off surgically. Removed tissues are sent to a pathology laboratory to identify the type of cancer involved. Skin cancer is mainly seen in older cats. It tends to show up on the legs, mouth, tongue base, lips, nose, ear tips, face, back and/or chest.
Basal Cell Carcinoma
Basal cell carcinoma usually presents as a solitary growth that may or may not be pigmented and occasionally ulcerates (bleeds). It can occur in clusters. Basal cell tumors can be found almost anywhere on cats and are especially common on the face, back and upper chest areas. Most feline basal cell tumors are benign, which means that they don’t spread. They still should be removed. Persian cats are predisposed to developing a malignant form of basal cell skin cancer; any bumps on a Persian should be taken seriously.
Squamous Cell Carcinoma
Squamous cell carcinomas, also called epidermoid carcinomas, typically present as ulcerated, crusty, weeping, necrotic, non-healing cauliflower-like or hard flat growths. They tend to show up on a cat’s ear tips, lips, nose, eyelids and in the mouth. They can be exacerbated by exposure to sunlight, especially in white or very lightly pigmented cats with pink skin. Complete surgical excision is the treatment of choice; radiation is helpful if the masses can’t be successfully removed. Chemotherapy is also an option.
Mast Cell Tumors
Mast cell tumors are fairly common, representing about 20% of all feline skin cancers. Young Siamese cats have a higher incidence of mast cell tumors than do other cats. These tumors can be single or multi-nodular growths that eventually release histamine and other irritating substances, causing gastrointestinal ulcers, skin lesions, itchiness and other symptoms. Mast cell tumors are most common on the belly, hind legs and scrotum. They can spread to other areas, such as the spleen. Mast cell masses should always be treated as soon as they are diagnosed. Treatment options include surgery, radiation, chemotherapy and administration of steroids.
Fibrosarcoma is an aggressive and highly invasive type of cancer that originates in fibrous connective tissue. In cats, it is often associated with the feline leukemia virus, the feline immunodeficiency virus or administration of vaccines. Fibrosarcomas tend to occur as solitary skin masses on the head, in the mouth, on the trunk or on the legs. There is some association between certain inactivated feline vaccines and development of fibrosarcomas at the injection site. However, the potential for vaccine-associated reactions shouldn’t deter owners from vaccinating their cats. Surgical removal of fibrosarcomas is often possible. However, without wide clean surgical margins, these tumors often recur.