Advances in veterinary diagnostics have increased the likelihood of diagnosing cancer during a cat’s life. Carcinogens like secondhand smoke, ultraviolet rays, and obesity are associated with an increased risk of cancer in cats, as in humans. Cancer is the leading cause of non-accidental death in cats. In cats, cancer is also commonly linked to a retrovirus, called feline leukemia virus.
What happens after a cancer diagnosis?
Treating and managing cancer in a feline patient is a team effort and involves the primary care veterinarian, the veterinary health care team, veterinary specialists, and the family. Treatment varies depending on the type and progression of cancer, but it may include surgery, chemotherapy, radiation therapy, or a combination of these treatments.
With any cancer management strategy in cats, optimal nutrition is essential. Proper nutrition can help a cat with cancer live longer and have a better quality of life.
What changes occur in the cat’s body when it has cancer?
In cats with cancer, their metabolism changes over time, passing through four phases:
- Phase 1 is pre-clinical, meaning cats show no outward signs of illness, although some blood test parameters may change. No blood test can screen and diagnose cancer in this early stage.
- In Phase 2, cats begin showing clinical signs of cancer, including decreased activity levels, a reduced or poor appetite, and possibly weight loss. Some signs are secondary effects of radiation therapy, surgery, or chemotherapy.
- In Phase 3, cancer-related metabolic changes cause a significant loss of muscle and fat stores. This profound loss of body condition is called cancer cachexia and may be reversible if remission is achieved. Remission is the complete disappearance of detectable cancer cells; the cat may or may not still show clinical signs.
- Phase 4 occurs in remission. Even though the cancer is eliminated, metabolic changes may persist, making a full recovery challenging. Nutrition is important for managing these metabolic changes.
How will cancer treatments affect my cat’s nutritional status?
The metabolic effects of cancer will persist after treatment. By anticipating the nutritional impacts of cancer treatment, you can work with your family veterinarian and/or a qualified veterinary nutritionist to adjust your cat’s nutrient profile and potentially avoid some negative side effects.
Surgery: The effects of surgery depend on the type of surgery performed. Head and neck surgery, for instance, may make it difficult for your cat to eat. A feeding tube can be lifesaving in this case and can be used for days, weeks, or months, if needed.
Cats undergoing stomach or intestinal surgery generally benefit from a complete and balanced diet that is higher in calories per cup or per can. The increased energy density allows the cat to eat a smaller volume of food while still getting the appropriate nutrients and calories. Kibble or wet foods (e.g., canned, pouches) that have a higher energy density are also highly digestible; some examples include kitten foods and veterinary therapeutic diets designed for the management of diabetes mellitus.
Chemotherapy: Chemotherapy directly affects rapidly reproducing cells. Cancer cells are the intended target, but other rapidly dividing cells can be affected, such as cells that line the stomach and intestines. The result is often nausea, vomiting, and diarrhea, which typically decrease a cat’s appetite and food consumption. Medications that control nausea and vomiting are often needed.
It is crucial to carefully monitor the cat’s daily water and Calorie intake to reduce the risk of dehydration and malnutrition. As mentioned, a complete and balanced diet with an increased energy density allows the cat to eat a smaller volume of food and still meet Calorie goals.
Radiation therapy: The nutritional complications of radiation therapy vary depending on the location and dose of treatment, as well as its reaction to other, simultaneous cancer treatments.
- Head and neck radiation is known to decrease saliva production and can cause ulcers in the mouth and throat, preventing normal eating.
- Radiation to the chest and upper abdomen can cause nausea and vomiting.
- Lower abdomen radiation can cause diarrhea.
In addition, radiation therapy is typically performed over successive days while the cat is under general anesthesia. A cat must be fasted for anesthesia (must not have any food), so the timing of feeding before and after treatment is important to avoid weight loss and muscle condition loss.
What nutritional changes should I consider for my cat with cancer?
Not all cats diagnosed with cancer require a diet change. The main goal when determining the best diet for a cat with cancer is to avoid weight loss, but also to avoid excess weight gain.
The first step is to work with your veterinarian to understand how many Calories per day your cat needs to maintain a stable body weight. About 90% of total daily Calories should go into the food bowl (divided into two or more meals), and 10% can be given as treats over the course the day. Limiting treats to 10% of total daily Calories prevents the diet from getting unbalanced.
The second objective when feeding a cat with cancer is to ensure the diet is palatable and easy to digest so the cat can meet its daily nutritional needs, which include more than three dozen nutrients. Some people recommend feeding cats with cancer a diet low in carbohydrates, hoping to limit the sugar that cancer cells use for energy. This idea comes from older research that shows tumors take up more glucose than normal tissues. However, newer studies show that cancer cells can adapt and use other nutrients, like fat and protein, when carbohydrates are limited.
"Certain cancers can alter the way proteins, fats, and carbohydrates are processed,
which affects a pet’s energy and muscle health."
Cancer research in cats has grown significantly over the past 20 years, and scientists now understand that cancer doesn’t just form tumors — it changes how the body uses nutrients. Certain cancers can alter the way proteins, fats, and carbohydrates are processed, which affects a pet’s energy and muscle health. Knowing this helps veterinarians design diets that support a cat’s immune system, organ functions, and overall well-being during treatment, rather than relying on one-size-fits-all approaches. Your veterinarian can help you choose a diet that that fits your cat’s specific needs, including nutrient profile, form (e.g., kibble, canned, pouches), and delivery method (particularly if there is a feeding tube involved).
If you wish to investigate feeding a homemade diet, your family vet should refer you to a qualified veterinary nutritionist who is experienced in using formulation software. Homemade diets must be balanced appropriately and recipes require some vitamin and mineral supplementation. Additionally, omega-3 fatty acids — eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) — may be recommended as supplements to fight inflammation, and veterinary nutritionists can advise on specific products and appropriate dosages.
Every cancer and every cat is different, so the diet should be regularly monitored. Whenever your cat is seen by the family vet or a consulting vet (e.g., oncologist or nutritionist), they should perform a nutritional assessment to determine if the cat’s risk for malnutrition has changed in any way. Adjustments to the diet or feeding management can be addressed at each evaluation.
