An early diagnosis provides the best chance for felines who may be suffering from cancer.

By Kate Eldredge Basedow, LVT
October 30, 2020
tabby cat gazing out the window
Credit: AzmanL / Getty

A cancer diagnosis is something no one wants to hear, whether it's for us humans or our beloved pets. But cancer is a real fear, and one that increases as we (and our pets) age. In fact, it's estimated that one in five cats will be diagnosed with cancer. So while it's wonderful that our cats are living longer lives, it means an increased risk that cancer could strike. Thankfully, progress in how we understand and treat cancer means there are more treatment options available that can help ensure our feline friends are kept healthy and happy for as long as possible.

What Causes Cancer in Cats?

“Cancer” and “neoplasia” are blanket terms for when cells in your cat’s body begin to divide and multiply out of control. This clump of poorly-behaved cells is a tumor, or neoplasm. Tumors can form anywhere in the body, and will look and act differently based on the original cells they came from.

Benign tumors are lumps that are growing where they aren’t supposed to be or beyond the bounds of that cell type’s normal territory, but that don’t invade other tissues or spread throughout the body. One of the most common forms of benign tumor in cats is a lipoma, or fatty tumor. While these squishy lumps can be unsightly, they usually grow slowly and don’t destroy neighboring tissue.

Malignant tumors invade and damage neighboring tissues and may also spread throughout the body. Tumor cells can break off and travel through the blood vessels and lymphatic system, forming a seed to start a new tumor elsewhere in the body. This secondary growth is called metastasis, and most commonly occurs in the lungs.

The cause of a cat’s cancer is often unknown. Some cancer types may have a genetic element and be inherited, and environmental factors and carcinogens can also play a role. We do know that the feline leukemia virus (FeLV) can cause lymphoma and leukemia in cats, and that feline immunodeficiency virus (FIV) is a risk factor for developing cancer. Thankfully, your vet can test for both of these viruses, and keeping your cat indoors can help protect her from contracting them! White cats have an increased risk of developing squamous cell carcinoma, particularly on their face and ears. In very rare cases, vaccination can lead to the formation of a fibrosarcoma—but it's a small chance. The Veterinary Information Network reports that studies have found only 1 in 1,000 to 1 in 10,000 vaccines will lead to formation of a fibrosarcoma—much less than the risk of contracting one of the diseases that vaccines protect against.

Signs and Symptoms of Cancer in Cats

Potential signs of cancer in cats include:

  • Bad breath or odor
  • Behavior changes
  • Diarrhea
  • Difficulty breathing
  • Drooling
  • Enlarged lymph nodes
  • Hiding
  • Icterus (yellow appearance to skin)
  • Lameness
  • Lethargy
  • Lumps
  • Pain and discomfort
  • Pale gums
  • Poor appetite
  • Snorting
  • Sores that don’t heal
  • Swelling
  • Vomiting
  • Weight loss

Many of these signs could apply to a number of conditions, but age can be a risk factor. Senior cats are more likely to have cancer than younger cats. Any time your cat seems off, especially if it persists for several days or more, she should be examined by a veterinarian to determine what is going on.

Most Common Types of Cancer in Cats

There are many types of cancer in cats. Each type is named for the cells from which the tumor originated. For example, lymphoma affects the lymphatic system, while osteosarcoma affects bone. For every type of cell in the body, from your cat’s skin to her stomach and blood vessels, there is a corresponding type of cancer. The cells most likely to become cancerous are ones that rapidly divide.

The most common sites for cancer in cats include:

  • Skin
  • White blood cells
  • Mouth
  • Gastrointestinal tract (stomach and intestines)
  • Mammary glands

Lymphoma is the most common cancer in cats. This is cancer of the lymphocytes (a type of white blood cell) and lymph node tissues. Enlarged lymph nodes are a hallmark of this cancer type, as well as weight loss, vomiting, and diarrhea. FeLV and FIV-positive cats are at increased risk.

Oral squamous cell carcinoma is the most common oral cancer in cats, and affects the cells that line the skin and mouth. This cancer can be very difficult to treat.

Cancer Diagnosis and Treatment

Diagnosis for cancer in cats will always start with a physical exam, and usually blood work as well. Blood work is extremely valuable for helping your veterinarian determine what might be wrong with your cat. Typical blood work includes a complete blood count (CBC) to evaluate your cat’s red and white blood cells, as well as her platelets, and a chemistry panel to evaluate organ function.

Radiographs (X-rays) and ultrasound are also frequently used to look for tumors. Tumors in more challenging locations, such as the brain, may require advanced imaging such as a MRI or CT scan. 

To get an accurate diagnosis, it is necessary to evaluate the tumor cells under a microscope. Your regular vet may do an initial investigation, but in most cases, it will be necessary to send samples out to a reference lab for a histopathology report. The lab will be able to determine the type of cancer. Depending on the location of the tumor, a fine needle aspirate (where the vet pokes the tumor with a needle to extract cells) may be sufficient, or your vet may do a surgical biopsy.

Staging determines the severity of the cancer, and takes into account information from the histopathology report, blood work, radiographs, and any other diagnostics done. Most cancer types are graded on a scale of 1 to 4, with Stage 4 being the worst. These cases usually have metastases to other parts of the body and the cat may be in poor condition.

Treatment depends on several factors:

  • Type and stage of cancer
  • Location of tumor(s)
  • Cat’s personality and tolerance for veterinary care
  • Financial constraints
  • Travel limitations

Discuss treatment options with your veterinarian. It is often beneficial to do a consultation with a veterinary oncologist at a specialty clinic to get the most up-to-date information on treatments and medications that may work for your cat.

The four primary options for treating cancer in cats are:

1. Surgery

This is a physical removal of the tumor. In some cases, surgery itself may provide a cure. In other cases, such as oral tumors, it may not be possible to remove the entire tumor. Debulking the tumor and removing as much as possible can still provide your cat with relief and improve her quality of life.

2. Chemotherapy

Chemo treatment is an administration of medications to kill the cancer cells. These medications generally target rapidly dividing cells, and can impact good cells that fit that profile as well. Exact side effects will depend on the drug and dosage given, but common side effects include bone marrow suppression, nausea, diarrhea, vomiting, and organ damage. Some drugs are given as injections while others are tablets. It is common to use combinations of chemotherapeutic medications to maximize effectiveness of the treatment while also minimizing the dose needed of each individual medication. Special care will need to be taken with the cat’s urine and feces after treatments to limit your exposure to these drugs.

3. Radiation

Strong radiation beams are directed at the tumor to kill the cancer cells, though radiation can also damage normal cells that get in the way. The cat will be put under anesthesia during treatments to ensure that she stays still during the treatment to minimize damage to healthy tissues. Depending on the machine and protocol used, it may be a one-time treatment, or require several sessions. The process itself doesn’t hurt, but radiation can cause skin irritation and hair loss. Your cat will not be radioactive after these treatments, so no special precautions need to be taken for your safety.

4. Hospice Care or Medical Management

Medical management of cancer means keeping your cat comfortable so she can enjoy the rest of her life. This is often the best option for cats who are extremely stressed by veterinary procedures or who are too ill or frail to undergo treatment. The cancer itself will not be addressed, but symptoms will be addressed to make your cat feel better. Some cases of cancer can be cured, while others can only be controlled or put into remission. Consider the potential side effects of your chosen treatment options, and how much time a given treatment might gain for your cat. There is no wrong answer—what is right for one cat may not be a good fit for another.

Living With a Cat Who Has Cancer

Keep a written record of your cat’s symptoms, diet, weight, treatments, and any side effects. This will allow you to track improvements or emerging issues to alert your vet. Pay special attention to signs that indicate her quality of life, such as how much she is eating and whether she still engages in activities that she enjoys. 

Depending on the type of cancer and treatment plan that you choose to pursue, your cat may receive pain medications to keep her comfortable. If she has a poor appetite, try warming her food to increase the odor. Appetite stimulants can also be given to encourage her to eat, or in some cases, your veterinarian may place a feeding tube to ensure that she is getting adequate nutrition even if she doesn’t want to eat. If she shows signs of nausea, she can be given medications to help her feel better.

Depending on how much her condition worsens over time, you may eventually have to make the very tough decision to euthanize your cat. Consider whether she has more good days or bad days, and whether she is suffering, as euthansia allows her to pass away peacefully.

No matter what health conditions your cat may develop, the best first step is to reach out to your pet’s veterinarian for an exam, advice, and next steps to care for your precious feline.