Veterinarian-written / veterinarian-approved articles for your cat.

Common Cancers in Cats

cat_ragdollCancerous tumors are masses of tissue that result when cells divide more rapidly than normal or do not die when they should.

Because tumors can develop from any tissue type, there are many types of tumors in many locations. As a cat owner, having the information about the tumor type and behavior can help you obtain the best treatment options to provide the greatest quality of life and longevity for your cat.

You should always check in with your family veterinarian if you find a new mass or swelling on your cat. Many times, your veterinarian can provide treatment at their clinic, but other times, they may refer you to a veterinary oncologist who specializes in the treatment of pet cancer.

Treatment of Cat Cancers

There are 3 primary ways in which cancers may be treated in cats. Surgery, chemotherapy, radiation therapy, or a combination of these treatments may be recommended in a treatment plan.

Because different tumors respond differently to each type of treatment, it is crucial that an accurate diagnosis and stage of advancement, determining what other organs are involved, be made by your veterinarian. This usually involves taking small samples of the tumor, either with a needle or a biopsy instrument, and sending the samples to a laboratory for analysis. Your veterinarian can then inform you whether the growth is benign or malignant and advise you about further treatment recommendations.

Some tumors may be cured by surgery alone. Others are more responsive to chemotherapy, which are drugs administered either by injection or orally. Radiation therapy is a third way to treat tumor cells that are sensitive this type of treatment. Radiation is often combined with other treatments, such as surgery.

Chemotherapy drugs work by damaging rapidly dividing cancer cells while sparing normal cells. Because of this, normal tissues that also rapidly divide, such as those found in the intestine, bone marrow, and hair, can be transiently negatively affected by chemotherapy. Many owners hesitate to pursue chemotherapy in their cats based on their knowledge of side effects in human cancer patients. It is important to remember that chemotherapy protocols are very different for cats than for humans. Veterinary oncologists have a different goal, which is to provide a good quality of life with minimal side effects. For this reason the doses of chemotherapy are lower in cats than in people and side effects are much less common. Should side effects occur, the drug doses are lowered for future treatments.

Below is some information on clinical signs, tumor behavior, diagnostic tests, and treatment options for the most common cancers seen in cats.

Lymphoma in Cats

Feline lymphoma, or lymphosarcoma, is one of the most common tumors seen in cats. There is a strong association between a cat being infected with feline leukemia virus (FeLV) and the development of lymphoma. When a cat develops lymphoma, the lymphocyte, which is a cell of the normal immune system, becomes cancerous and can affect multiple areas of the body. Because of the potential for widespread infection, the classification feline lymphoma is often divided into several forms. These include:

  1. Multicentric (many different organs involved)
  2. Gastrointestinal (digestive)
  3. Mediastinal (lymph nodes in the chest)
  4. Renal (kidney)
  5. Spinal (brain or spinal cord)
  6. Nasal

These forms differ from each other in the average age of diagnosis, clinical signs your cat may exhibit, recommended treatment, and association with FeLV. Multicentric, gastrointestinal, and nasal forms of the disease tend to affect middle-aged cats and are not usually associated with feline leukemia virus. Mediastinal and spinal forms usually affect younger cats that are between 2 to 3 years of age and are also infected with feline leukemia virus. Cats with the renal form of the disease may be positive for FELV and are usually middle-aged with an average age of 8 years old at the time of diagnosis.

If your cat is diagnosed with lymphoma, your veterinarian will recommend several tests including x-rays, urinalysis, complete blood count, chemistry profile and possibly an ultrasound. These tests provide information for staging the tumor. Staging allows your veterinarian to determine the extent of the disease and the long term outlook, or prognosis, for your cat.

Treatment of feline lymphoma is generally a combination of chemotherapy using multiple drugs on a rotating schedule. Some of these drugs are given by injection in the hospital setting and others orally at home. Nasal lymphoma is the exception, in which radiation therapy may also be recommended in addition to chemotherapy.

Squamous Cell Carcinoma in Cats

Squamous cell carcinoma is a cancer that frequently develops on areas that are non-pigmented or lightly pigmented in the cat. This is similar to the development of skin tumors in pale-skinned people. In the cat, these areas tend to be on the tips of the ears (pinnae), the nasal areas, and the eyelids. Squamous cell carcinoma represents 15% of all skin tumors in cats.

Cats with frequent sun exposure may first develop a condition called solar dermatitis (actinic dermatitis) in areas that are lightly pigmented. This may show up as pink areas of skin with some scaling. If your cat is diagnosed with this condition, your veterinarian will probably recommend sun restriction and application of a water-based sun screen on the affected area twice daily. If the condition worsens, the skin may develop more of a cauliflower-type growth and have open or ulcerated wounds that can bleed. At this stage, your veterinarian is likely to recommend biopsy of the area to determine if cancer, likely squamous cell carcinoma, is developing.

The severity of squamous cell carcinoma in cats is often dependent on how quickly treatment is administered, so seeking help for your cat as soon as signs develop is strongly recommended. The tumors can spread locally, affecting adjacent tissues, but long term, if left untreated, it can spread to distant areas like lymph nodes or lung tissue.

Treatment of squamous cell carcinoma in cats is dependent on the areas involved, but it usually starts with surgical removal of the tumor. This works well on areas such as the ears but can be tricky with other locations such as nasal areas or eyelids. Your veterinarian will likely refer you to a surgical or cancer specialist (veterinary oncologist) for all treatment options. Such options include radiation therapy, cryotherapy, laser therapy, and photodynamic therapy.

Soft Tissue Sarcomas in Cats

Sarcomas are a large group of tumors that all originate from structural and connective tissues. They go by many names, including fibrosarcoma and vaccine-associated sarcoma, but they are all similar in their behavior and treatment. Although sarcomas are not a new type of tumor, there has been increased research recently done on them by the veterinary community. In 1991, veterinarians noticed a huge increase in the incidence of soft tissue sarcomas at the sites of vaccinations (such as on the rear limbs or between the shoulder blades). A task force was created that has done much work to make vaccines safer for cats and recommend alternative sites for vaccine administration. Today, veterinarians generally administer vaccines lower on the hind limbs and instruct owners to monitor the site for development of masses at the site to catch any tumor growth early.

Sarcomas tend to spread locally by invading adjacent tissues via finger-like projections under the skin. As an owner, you may notice a small, firm mass on or under your cat’s skin, but beneath the surface, this tumor may have reached areas 3 centimeters from what you can see or feel. If caught early, sarcomas do not usually spread to distant areas and have only an 11-20% reported metastatic rate.

Treatment for soft tissue sarcomas depends on the tumor size and location. The best outcome for your cat is to catch a tumor early and have aggressive surgery performed. Depending on the area affected and size of the tumor, your veterinarian may refer you to a surgical specialist because often deep and extensive tissue (including muscle and bone) has to be removed for complete cure. Occasionally, radiation therapy may be recommended either before or after surgery if there has been extensive spread of disease. If the tumor is not completely removed, the chance of regrowth is high, with one study reporting average time of regrowth being 3 months after surgery. Chemotherapy is rarely recommended in treatment plans for sarcomas.

Mammary Gland Carcinomas in Cats

Mammary tumors are most commonly diagnosed in older cats between 10 and 14 years of age. Unlike other species, the feline mammary tumor is very aggressive, with 80-90% of all tumors found to be malignant. For this reason, the prognosis for cats diagnosed with a mammary tumor is usually poor.

Mammary carcinomas tend to be locally invasive, meaning they spread into adjacent tissues. They also have the potential to spread to distant sites or metastasize. Strategies for treatment are aimed at local control (surgery) and distant control (chemotherapy). Your veterinarian will initially recommend removal of the tumor with a surgery called a radical mastectomy. Depending on the outcome of the surgery and the biopsy results, you may also be advised to consider chemotherapy following surgery.

Prognosis for mammary gland carcinomas depends on the size of the tumor at diagnosis as well as the biopsy results or tumor grade. Tumors that are greater than 3 centimeters in size are often associated with survival times of 6 months, while tumors less than 2 centimeters often afford survival times of 3 years after surgery.

According to an article on the American College for Veterinary Surgeons: Cats spayed before 6 months of age have a 7-times reduced risk of developing mammary cancer, and spaying at any age reduces the risk of mammary tumors by 40% to 60% in cats. (http://www.acvs.org/AnimalOwners/HealthConditions/SmallAnimalTopics/MammaryTumorsinCatsandDogs/)

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