At a glance
What is cancer?
Cancer is the uncontrolled division of cells within the body and can affect all types of cell. It can affect cats of any age but is typically seen in middle-aged to older cats. We take a look at some of the more common types of cancer, their symptoms, and how it is treated.
Several predisposing factors can increase a cat’s chances of developing cancer, such as exposure to chemicals, second-hand smoke, certain viral infections (feline leukemia virus and feline immunodeficiency virus) and obesity.
Top five cancers in cats
The most common form of cancer in cats, lymphoma is a cancer of the lymphoid tissue caused by the abnormal growth of lymphocytes (a type of white blood cell). Lymphoma can develop in many parts of the body, but it affects the gastrointestinal tract most often.
- Viral infections (FIV and FeLV): Cats with feline leukemia virus are 60 times more likely to acquire lymphosarcoma than those without. Cats with FeLV are 5-6 times more likely to develop lymphosarcoma
- Immunosuppressive drugs
- Genetics: There is a higher incidence in Manx, Siamese, and Burmese cats
- Chronic inflammation
- Environmental: Cats living in smoking households are twice as likely to acquire lymphosarcoma
Clinical signs of lymphosarcoma vary depending on the organ/tissues involved. The gastrointestinal system is most commonly affected.
Squamous cell carcinoma
Squamous cell carcinoma (SCC) is a type of cancer that originates in the squamous epithelium, the layer of cells covering the external surfaces, the mucosa of the mouth and lines the hollow organs (lungs, esophagus, bladder, and stomach). Although SCC’s are rapid growing tumours and locally invasive, they are slow to metastasise (spread) to other parts of the body.
There are three types of SCC in cats:
- Oral – Affecting the tissues in the mouth
- Skin – Ears, nose, lips, temples, and eyelids are the most common areas
- Bowen’s disease – A skin cancer occurring in multiple locations on the skin
- Small raised red dots on the affected area which slowly increase in size into scaly red patches which crust and bleed
- Non-healing sores on the nose or face
- Scabs along the ear margins which may ulcerate
- Hair loss in the affected area
- Tissue erosion is common as the tumour progresses into the deeper tissue layers
- Lump in the mouth
- Bad breath
- Reluctance to eat, which in turn can lead to slow and progressive weight loss
- Dropping food when eating
- Swelling of the upper or lower jaw
- Loose teeth
- Oral pain
- Multiple sores on the head and body
- Dried crusty areas, especially on the head
Mammary gland tumours are similar to breast tumours in people; it is the third most common tumour in senior cats. 80-90% of mammary gland tumours are malignant; adenocarcinomas are the most common type of malignant tumour of the breast in cats.
The average age of cats with mammary gland tumours is 10-12 years old.
Intact females are at the greatest risk and spaying (desexing), especially before their first heat, can greatly reduce their risk of mammary cancer. This suggests a hormonal influence may be involved. However, it can also occur in spayed females and males, but it is rare. Siamese cats appear to be at an increased risk of developing mammary gland tumours at a younger age.
- Painless, firm, nodular mass in one or more mammary glands
- Ulceration of the skin
- Infection, swelling, and pain
Fibrosarcomas (FSA) is an aggressive type of malignant growth (cancer) that consists of fibroblasts that originate in the fibrous connective tissue. They are the most common soft tissue tumour to affect cats.
There are three causes of fibrosarcoma in cats:
- Age: Fibrosarcomas are common in older cats. The cause has not been established, although cancers more common in older cats. This is usually a single, irregularly shaped mass found on the trunk, legs, and ears.
- Vaccinations: The use of vaccines is known to cause fibrosarcoma (vaccine-induced sarcoma or vaccinosarcoma). Most commonly, due to rabies and Feline Leukemia vaccines. The protocol for vaccinations now is to give the rabies vaccine in the rear right leg and the feline leukemia vaccine in the rear left leg, so if a fibrosarcoma does develop, the affected limb can be amputated. The prevalence of VAS is 1:1000 – 1:10 000 for FeLV and rabies. These types of fibrosarcomas are commonly more aggressive. The cause of VAS is believed to be the adjuvant within the vaccination; this is a substance (usually aluminium) that keeps the killed virus in the localised area for some time to give the body the chance to stimulate an immune response. This can result in localised inflammation, and possibly the formation of fibrosarcoma.
- Feline Leukemia Virus: A mutant form of FeLV (feline sarcoma virus) also causes fibrosarcoma. This occurs in younger cats as multiple tumour masses. Cats under four are usually affected.
Fibrosarcomas are most commonly located on the trunk, neck, legs, ears and oral cavity. Symptoms can vary depending on the location of the tumour but may include:
- Localised soft tissue swelling. This may be firm, poorly circumscribed (irregular) and measure between 1-15cm. Ulceration may develop in advanced cases.
- Cats with oral fibrosarcomas may have difficulty eating and swallowing, bad breath and drool. Lumps may or may not be painful.
- Fibrosarcomas of the limbs may cause limping, swelling and tenderness.
As cancer progresses, other symptoms such as anorexia (loss of appetite), weight loss and lethargy may occur.
Osteosarcoma (osteogenic sarcoma) is an aggressive and destructive type of primary cancer that develops in the bones. It is the most common type of bone cancer in cats and accounts for 70% of bone tumours. Cancer arises from osteoblasts or osteoclasts, which are cells that produce a matrix that builds or breaks down bone. Osteosarcoma may either be osteoblastic (bone-forming) or osteolytic (bone dissolving).
- Localised pain and swelling
- Limited range of motion of the affected limb
- Muscle wastage around the affected area
- Difficulty chewing if the cancer is in the jaw
- Fractures may occur when there has been little trauma to the bone or may be severe than one would normally expect
- Nosebleed if the cancer is in the nasal bones
- If the cancer is in the pelvis, your cat may experience difficulty defecating as the pelvis narrows
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 an obvious growth. Microscopic evaluation of the tumour is necessary for a definitive diagnosis.
- Baseline tests: Complete blood count, biochemical profile 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 an obvious growth, your veterinarian will take a biopsy which will be sent to a laboratory for 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.
- 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 that 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 impulses into the tumour after administration of chemotherapy. More information can be found on this site.
- 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.
Not all cancers are preventable, but some are. Below are a few ways we can help to reduce the chances of a cat developing cancer.
- Desex your cat, this eliminates testicular, ovarian and uterine cancer and greatly reduces the chances of mammary cancer.
- Reduce the number of chemicals in the home, where possible, switch to natural alternatives such as white vinegar or bicarbonate of soda.
- Avoid sun exposure, especially in thin coated or pale cats.
- Avoid over-vaccination, current guidelines recommend three vaccinations for kittens between 8-16 weeks, followed by a booster at 12 months and then every three years for low-risk cats. This protocol may vary in some parts of the world where compulsory vaccinations such as rabies are a requirement.
- Do not smoke around your cat.
- Keep your cat’s weight down as obesity can contribute to several cancers.
- Schedule annual check-ups for all cats aged 0-7 and then bi-annual, this can help to pick up diseases, including cancer early on, which can in many cases make treatment easier.