Signs of Cancer in Cats: Early Warning Signs Every Owner Should Know

Signs of Cancer in Cats: Early Warning Signs Every Owner Should Know

Cancer is the leading cause of death in cats over age 10, yet it's often caught late because cats hide illness so effectively and because many cancer signs are subtle or easily attributed to aging. Knowing the warning signs — and acting on them promptly — can make a significant difference in treatment options and outcomes.

How Common Is Cancer in Cats?

• Cancer accounts for approximately 32% of deaths in cats over age 10
• Lymphoma is the most common cancer in cats, followed by squamous cell carcinoma and mammary tumors
• Unlike dogs, cats are more likely to develop malignant (aggressive) tumors — approximately 85% of mammary tumors in cats are malignant
• Early detection significantly improves treatment success rates

The 10 Warning Signs of Cancer in Cats

1. Unexplained Weight Loss

Progressive, unexplained weight loss is one of the most consistent signs of cancer in cats. Cancer cells consume significant energy and alter metabolism, causing weight loss even when appetite seems normal. Any cat losing weight without an obvious dietary cause should be evaluated promptly.

2. Lumps, Bumps, or Swellings

Any new lump, bump, or swelling under the skin warrants veterinary evaluation. Not all lumps are cancerous — but all should be assessed. Perform a monthly at-home body check by running your hands gently over your cat's entire body, feeling for any new masses, asymmetry, or areas of firmness.

Pay particular attention to:

• The mammary glands (two rows of nipples on the belly) — mammary tumors are common and aggressive in cats
• The neck and jaw area — lymph node enlargement
• The abdomen — internal masses may be palpable
• Injection sites on the shoulder blades — injection-site sarcomas, though rare, can develop here

3. Sores That Don't Heal

Non-healing sores, ulcers, or wounds — particularly on the face, ears, nose, or mouth — can indicate squamous cell carcinoma or other skin cancers. White or light-colored cats are at higher risk for sun-related skin cancers on the ears and nose.

4. Changes in Appetite

Both decreased and increased appetite can signal cancer. Gastrointestinal lymphoma (the most common form in cats) often causes reduced appetite, weight loss, and digestive symptoms. Oral tumors cause pain that makes eating difficult.

5. Difficulty Eating, Swallowing, or Drooling

Oral tumors — particularly squamous cell carcinoma of the mouth — are common in cats and cause significant pain. Signs include:

• Dropping food while eating
• Chewing on one side only
• Excessive drooling, sometimes blood-tinged
• Bad breath that's worse than usual
• Reluctance to eat hard food
• Visible mass or discoloration in the mouth

6. Persistent Vomiting or Diarrhea

Chronic or recurring vomiting and diarrhea that doesn't respond to standard treatment can indicate gastrointestinal lymphoma or other GI tumors. This is one of the most common presentations of feline cancer.

7. Difficulty Breathing

Labored breathing, rapid breathing, or open-mouth breathing can indicate chest tumors, pleural effusion (fluid around the lungs from cancer), or lung metastases. Any breathing difficulty is a medical emergency.

8. Lethargy and Reduced Activity

A cat that is significantly less active than usual, sleeping more, or showing reduced interest in play and interaction may be experiencing cancer-related fatigue, pain, or metabolic changes.

9. Changes in Litter Box Habits

Straining to urinate or defecate, blood in urine or stool, or changes in frequency can indicate tumors of the bladder, colon, or reproductive organs.

10. Neurological Signs

Seizures, loss of balance, head tilting, circling, or sudden behavioral changes can indicate brain tumors or cancer that has spread to the nervous system.

Cancer-Specific Signs by Type

At-Home Monitoring

Monthly at-home checks help you catch changes early:

• Run your hands over your cat's entire body feeling for lumps or asymmetry
• Check the mouth for masses, discoloration, or unusual odor using a medical penlight
• Weigh your cat weekly — track on a simple log
• Monitor litter box output for blood or changes
• Use the KIT4CAT CheckUp At-Home Wellness Test Kit to check urine for blood and protein

When to See the Vet

Schedule a vet appointment promptly if your cat has:

• Any new lump or swelling
• Unexplained weight loss
• Non-healing sores
• Persistent vomiting or diarrhea
• Difficulty eating or drooling
• Any breathing difficulty (emergency)
• Neurological signs (emergency)

Annual wellness exams with bloodwork for cats over 7 — and twice-yearly for cats over 10 — are the best way to catch cancer and other serious conditions early.

Final Thoughts

The signs of cancer in cats are often subtle and easy to miss. Regular at-home monitoring, monthly body checks, and annual veterinary wellness exams are your best tools for early detection. When something seems off with your cat — trust your instincts and get them checked. Early detection saves lives.