"Cancer" is defined as any malignant cellular tumor. This definition must be broken down to be understood. A "tumor" is a swelling or other new growth of tissue caused by uncontrolled and progressive cell multiplication. Tumors can be benign or malignant. "Malignancy" is defined as the tendency of something to progressively worsen and to result in death, usually accompanied by properties of invasiveness and metastasis. "Metastasis" is the transfer of disease from one part of the body to another part that is not directly connected with it – essentially, a migration of cells into neighboring or remote tissues. Putting these definitions together, the term "cancer" encompasses a group of diseases that involve an uncontrolled and progressive transformation of normal cells into abnormal ones that becomes invasive, progressively worsens and ultimately spreads. Another word for cancer is "neoplasia." Feline neoplasia tends to strike older and intact animals. An exception to this is in cats infected with the feline leukemia virus (FeLV) or the feline immunodeficiency virus (FIV). These cats have an increased risk of developing cancer at a young age.
How Cancer Affects Cats
Cancer is among the leading causes of death in cats. This probably is at least partially due to the fact that companion cats are living longer with continual improvements in nutrition and veterinary care. How cancer affects a particular cat depends upon the type of cancer and the biological make-up of the individual animal. Meaningful generalizations about the effects of cancer cannot be made. Ultimately, most untreated or untreatable malignancies will hasten death.
Causes of Cancer in Cats
Medical science has not yet determined the precise causes of the many forms of cancer in companion animals, despite intensive research in both the animal and human realms. Many different cancers occur in cats, including most commonly lymphoma, fibrosarcoma, mammary tumors, mast cell tumors, squamous cell carcinoma and other soft tissue sarcomas, among others. Each of these can present in multiple ways, with varying frequencies and degrees of severity. Certain cat breeds are predisposed to developing certain types of cancers. Spaying or neutering may reduce the risk of feline neoplasia.
Preventing Feline Cancer
Little is know about the prevention of cancer in companion animals. Once the underlying causes of the various cancers are ascertained, prevention will become more plausible.
Early diagnosis and treatment of cancer always improves the prognosis. Surgery, radiation and chemotherapy are available at specialized veterinary hospitals to treat cancer in companion cats. With prompt diagnosis, aggressive treatment and ongoing management, including pain management and dietary support, many cats with cancer can live long, comfortable and relatively normal lives.
Our feline friends may not look like us, but mammals are mammals, and cats suffer from some of the same diseases and medical conditions that affect people. Unfortunately, cancer is one of them and is one of the leading causes of feline death. The increasing number of diagnosed cancer cases in cats is probably due largely to the fact that cats are living longer with our significant improvements in companion animal nutrition and overall health care. Nonetheless, any prominent or persistent mass should be evaluated for malignancy.
Common Types of Cancer in Cats
The most common types of feline neoplasia are lymphoma, mammary cancer, basal and squamous cell carcinoma, mast cell tumors and fibrosarcoma.
Lymphoma is a general term applied to the system-wide and malignant neoplastic transformation of lymphoid tissue. It is the most commonly treated systemic cancer in veterinary medicine and is the most common hematopoietic malignancy in cats ("hematopoietic" means pertaining to or affecting the formation of blood cells). Lymphoma is very aggressive and frequently affects multiple lymph nodes, the spleen, liver, gastrointestinal (alimentary) tract and/or bone marrow. The symptoms of feline lymphoma depend upon what type of lymphoma the cat has and the particular organs affected. If diagnosed and treated early, lymphoma normally can be well-managed. Many cats achieve complete remission following chemotherapy. Without treatment, however, the prognosis is very poor. Feline lymphoma is seen more often with cats that are infected with the feline leukemia virus (FeLV) or the feline immunodeficiency virus (FIV). It also is more common in house cats exposed to chronic environmental tobacco smoke.
Feline Mammary Neoplasia
Tumors of the mammary glands are common in intact female dogs but less so in cats. Still, they represent the 3rd most common tumor type in cats. They most frequently affect older intact queens; Siamese cats are reported to have twice the risk of developing mammary cancer as all other cat breeds combined. Most of these tumors are adenocarcinomas that tend to present on the anterior (front) rather than the posterior mammary glands. In cats, approximately 90% of mammary masses are malignant and require aggressive surgical removal. The outlook for cats with mammary cancer is usually guarded, and depends largely upon how early the cancer is diagnosed and the success of aggressive treatment.
Skin and Subcutaneous Cancer in Cats
Soft tissue sarcomas are a group of tumors which arise from connective tissue and are classified together because of their similar biologic behavior and recommended treatment protocols. Feline skin tumors can be caused by a number of neoplastic processes. The most common forms of skin cancer in cats are basal cell carcinoma, squamous cell carcinoma, mast cell tumors and fibrosarcoma. Depending upon the cause of the mass, it may be small or large, soft or firm, grow quickly or slowly, be above or beneath the skin and be solitary or clustered with other masses. Many skin tumors metastasize if not promptly removed. These tumors are more common in middle-aged to older cats, and no evidence of direct genetic inheritance has been reported at the time of this article. Soft tissue sarcomas tend to show up spontaneously in cats and appear as firm masses on the legs, mouth or chest often appearing to be on top of, or right under, the skin. The goal of treating soft tissue sarcomas is complete eradication and removal.
Basal Cell Carcinoma
Basal cell tumors typically are solitary nodules that are frequently pigmented and occasionally ulcerated in cats. While usually localized on dogs, basal cell tumors can be found almost anywhere on cats. They are the most common type of feline skin tumor. Most feline basal cell tumors are benign, but when they are definitively diagnosed as carcinoma, they should be removed swiftly and aggressively, with wide surgical margins.
Squamous Cell Carcinoma
Squamous cell carcinomas frequently present as ulcerated, non-healing, crusty, weeping and necrotic sores. In cats, they tend to show up on the ear tips, lips, nose, oral cavity and eyelids and are the most common feline tumor in these areas. They can be exacerbated by exposure to ultraviolet light, especially in white or very lightly pigmented cats with pink skin. Complete surgical excision is the treatment of choice, with radiation if surgical margins are incomplete. Chemotherapy is also an option.
Mast Cell Tumors
Mast cell tumors (MCTs) are fairly common in cats, representing about 20% of all feline skin neoplasms. Siamese cats under 4 years of age have a higher incidence of mast cell tumors than do other feline breeds. These tumors are abnormal accumulations of mast cells that form nodular tumors which, when the mast cells degenerate, release histamine and other irritating substances that can cause or contribute to gastrointestinal ulceration, cutaneous lesions (including itchiness) and systemic clinical signs. Mast cell tumors have the potential to become malignant and metastasize to other sites. Therefore, they should always be treated immediately when diagnosed. Treatment options include surgery, radiation, chemotherapy and immunosuppressive steroid administration. The appropriate treatment protocol will depend upon the diagnostic stage of the tumor(s) and the veterinarian's particular recommendations.
Fibrosarcoma typically originates in subcutaneous connective tissue. In cats, this tumor is more common in association with feline leukemia virus, feline immunodeficiency virus and as vaccine-site-associated reactions. Fibrosarcoma tends to show up as solitary tumors on the head, in the mouth, on the trunk or on the legs. For some reason, there is a strong association between certain inactivated feline vaccines and development of soft tissue fibrosarcomas at the injection site. Fortunately, injection site fibrosarcomas are not common in cats. Unfortunately, feline fibrosarcomas can be extremely invasive and aggressive. While surgical removal is possible, without wide and clean surgical margins the masses often return. The potential for vaccine-associated fibrosarcomas should not deter owners from vaccinating their cats. Oral fibrosarcomas are the second most common oral malignancy in cats (second only to squamous cell carcinoma) and are highly invasive into surrounding bone.
Although a diagnosis of cancer is never good, timely detection, treatment and management of feline cancer can be remarkably successful.
Treating Cancer in Cats
There are a number of treatment options available for cats with cancer including surgery, chemotherapy and radiation. Early diagnosis and treatment will improve the chances of remission.
Surgery is the treatment of choice for most feline cancers. Localized masses often can be removed and, when detected early, the procedure carries an excellent success rate. Upon removal, the veterinarian will evaluate how aggressively the cancer has spread to other organs in the cat's body and will use this information to assess the outlook for the animal and establish a prospective course of action. The removed tissue will be submitted to a pathology laboratory for accurate determination of the exact type of cancer involved and whether appropriate surgical margins were obtained when the tissue was removed.
In cases where feline tumors are inoperable, other treatment options may be available, including radiation, chemotherapy and/or other biological therapies. During radiation therapy, malignant cells are killed by exposure to high levels of radiation. Chemotherapy involves administration of systemic medications designed to kill rapidly-reproducing cells, including cancer cells, while hopefully sparing most normal healthy cells. In some cases, the treating veterinarian may pursue a combination of therapies, such as surgery together with radiation or chemotherapy, in an attempt to arrest progression of the disease. One of the possible down-sides of radiation and chemotherapies is that normal cells will be adversely affected by the treatment. The goal of course is to eliminate all cancerous cells, but it is not presently possible to completely isolate healthy tissue from cancerous tissue through these treatments.
Supportive Cancer Therapies
Modern cancer management in cats involves far more than surgical, radioactive or chemical removal of cancer cells. Nutritional support, pain management, medical therapies for ulcer prevention, physical therapy and other supportive care techniques are all key components of a comprehensive treatment protocol designed to maintain an affected cat's quality of life.