At a glance
What is cancer?
Also referred to as malignant neoplasms or malignant tumours, cancer is the uncontrolled division of cells that normally should be restrictive in their growth. Tumours fall into two categories, malignant (cancerous) and benign.
- Benign tumours are slow-growing and surrounded by a capsule. They do not invade neighbouring tissue or spread (metastasise) to other areas.
- Malignant tumours, on the other hand, tend to grow rapidly, invade surrounding tissue and spread to other parts of the body.
Cancers are often described by the part of the body they originate from, for example, breast, brain, liver, bile duct or pancreatic cancer.
The disease can develop in cats of any age; however, it occurs most often in middle-aged to older cats. It is a leading cause of death in elderly cats.
How does cancer kill a cat?
Cancer cells divide unchecked and can spread (metastasise) to other parts of the body via the blood or lymphatic system.
- Bone marrow: Crowds out healthy stem cells which are responsible for the production of red and white blood cells, as well as platelets all of which are vital for life. Red blood cells transport oxygen around the body, white blood cells defend the body against organisms, and platelets are responsible for blood clotting.
- Gastrointestinal tumours can clog up the GI tract and prevent the movement of food through the GI tract where it would normally be digested to provide nutrients to the cat, which leads to malnutrition.
- Brain tumours take up space but the skull is not able to enlarge and the tumour increases pressure inside the cat’s head. This increase in pressure causes a host of symptoms including seizures and paralysis and impact on the brain’s ability to control many body functions.
- Lungs: Primary or metastatic cancer can cause death by infection or impact the lungs ability to function properly by killing off healthy lung tissue or creating blockages.
- Liver cancer (primary or metastatic) affect its ability to detoxify the blood which leads to a build-up of toxins in the blood and brain.
Some cancers, such as cancers of the skin would not be lethal if they didn’t metastasise, it is the spread of these cancers to other, critical organ systems which is what makes them so dangerous. Each type of cancer acts differently, some are fast-growing and metastasise early and others are slow-growing and less likely to spread to other body systems.
Classification of cancers
- Carcinoma originates from the epithelial cells which line the inner and outer parts of the body and can be split into two types. Adenocarcinoma originates in an organ or gland and squamous cell carcinoma which originates in the squamous epithelium.
- Leukemias cancers of the blood cells
- Lymphoma originates from the lymphoid tissue
- Myeloma originates from the cells in the bone marrow
- Sarcoma originates from the connective or bone tissue
Common cat cancers
The cause of most cancers is unknown, however, there are a number of contributing factors that can increase a cat’s risk of cancer.
- Carcinogens (agents which can cause cancer): Examples of carcinogens include UV radiation, X-Rays, certain chemicals, environmental toxins, cigarette smoke.
- Viruses: In particular, feline leukemia virus and feline immunodeficiency virus (lymphoma, squamous cell carcinoma).
- Genetic predisposition: Some lines of cats and breeds have a higher incidence of cancer.
- Injections: Originally called vaccine-associated sarcoma, the use of injections (especially vaccinations) have been associated with a rare form of cancer re-named injection site sarcoma.
- Obesity: Obesity is defined as cats who are 20% above optimal body weight which increases the risk of many diseases including several types of cancer.
Cancer symptoms will vary depending on the location and part of the body affected by cancer.
- Change in bowel or bladder habits (constipation, diarrhea etc.)
- Loss of appetite
- Unexplained weight loss
- Blood in urine or feces
- Abdominal pain
- Difficulty breathing
- Unexplained bleeding
- Lameness due to primary bone cancer or metastasis
- Difficulty eating (due to oral cancer)
- Lumps, bumps, crusty lesions on any part of the body
- Swollen lymph nodes
- Vomiting (sometimes with blood)
- Sores or ulcers that don’t seem to heal
- While rare, cats with pulmonic neoplasia (lung cancer) can develop a condition known as lung-digit syndrome where cancer spreads to the digits of the feet resulting in bone lysis (destruction). Cats present with lameness, swelling of the toes and pain.
Your veterinarian will perform a complete physical examination of your cat and obtain a medical history from you. It may be possible to make a presumptive diagnosis if there is a visible growth; however, evaluation of the tumour is necessary for a definitive diagnosis.
- Baseline tests: Biochemical profile, complete blood count, and urinalysis to evaluate the overall health of your cat and look for signs of infection or inflammation.
- Fine needle aspirate: The veterinarian uses a thin needle to remove a small sample from the abnormal tissue for microscopic evaluation.
- Biopsy: If there is a visible growth your veterinarian will take a biopsy for microscopic evaluation.
- Imaging: X-rays, ultrasound, computed tomography (CT) scans or magnetic resonance imaging (MRI) to evaluate the internal organs and look for tumours inside the body and signs of metastasis.
- Barium studies: Barium is a radio-opaque compound that when consumed coats the lining of the intestinal tract and shows the structures as white on x-rays. This test can be a useful diagnostic for cancers of the gastrointestinal tract.
Treatment may vary depending on the type and location of cancer.
- Surgery: Where possible, surgical excision of the tumour with a margin. It may also be necessary to remove lymph nodes closest to the tumour.
- Chemotherapy: Several drugs which target rapidly dividing cells. Chemotherapy can shrink a tumour before surgery, after surgery to kill cancer to kill any cells left behind, or as a stand-alone treatment where surgery is not possible. In the latter case, the goal is to slow down the progression of the tumour.
- Electrochemotherapy: An emerging therapeutic which shows great promise for the treatment of skin tumours. Chemotherapy drugs are poorly absorbed, but this treatment allows for better penetration by delivering electric impulsions into the tumour after administration of chemotherapy.
- Radiotherapy: A treatment that uses a radiation beam to target cancer cells. Radiotherapy can be used to treat cancers that cannot be surgically removed or after surgical removal to target any cancer cells which have been left behind.
- Cryosurgery: For the treatment of some cancers on the skin, liquid nitrogen is used to freeze and destroy target cancer cells.
Cats tolerate chemotherapy well, and it doesn’t cause hair loss but can cause lethargy for a day or two after treatment.
It is not always possible to prevent cancer in cats, but there are certain things we can do to reduce the chances of some types of cancer.
Spay and neuter: Spayed and neutered cats don’t roam as much or get into fights, reducing the chances of contracting FIV or FeLV. Intact females are at higher risk of developing mammary cancer than spayed females and castration eliminates a male cat’s chances of developing testicular cancer.
Avoid household chemicals: We can’t avoid the use of certain treatments to prevent parasites, nor should we, routine parasite control is vital. These are not effective where proper disinfection is necessary, but the average home uses a lot of chemicals.
Avoid over-vaccination: There has been a lot of talk about over-vaccinating our cats over the past ten years, only you and your veterinarian know your cat’s circumstances, but it is a discussion you should have. The new recommendation by the Australian Veterinary Association as well as the American Association of Feline Practitioners (page six) is to give your low-risk, household cats their core vaccinations (F3) as a kitten.
Three vaccinations are spaced 4 weeks apart at 8, 12 and 16 weeks, followed by a booster at 12 months and then every three years. This can reduce the risks of injection site sarcoma. Local regulations or individual risk factors may warrant more frequent vaccination as well as the administration of some non-core vaccinations.
The Australian Veterinary Association (AVA) believes that in most cases, core vaccines need not be administered any more frequently than triennially and that even less frequent vaccination may be considered appropriate if an individual animal’s circumstances warrant it. However, local factors may dictate more frequent vaccination scheduling. These recommendations may be ‘off label’ for some vaccines.
Limit sun exposure: Try to keep cats inside between the hours of 10 am – 4 pm, this is even more important if your cat is white or pale cats. Provide access to a shady area so that the cat can get out of the sun. If you notice any redness or damaged tissue, especially around the ears, seek veterinary attention.
Smoke outside: Cigarette smoke is a carcinogen in both cats and humans.
Schedule annual checkups: Even if you decide to go with triannual vaccinations, it is still important your cat see a veterinarian at least once a year.
See a veterinarian if you notice any lump larger than a pea, which has been present for longer than a month.
Keep the weight down: Obesity causes several health disorders and has been linked to the development of certain cancers.