Symptoms Of Cancer In Dogs And Cats
About 50% of senior dogs develop cancer during their lifetimes. The rate in cats is lower but still significant. Just as with people, pets can develop many different types of cancer, and early detection often improves the range of treatment options and outcomes.
Some signs of cancer are more specific and should prompt a veterinary visit right away. Others—such as weight loss, reduced appetite, or changes in activity—are more general and can signal many conditions. If you notice any persistent or unusual changes in your pet’s health or behavior, schedule an exam with your veterinarian to determine the cause and begin appropriate care.
3 Typical Cancer Symptoms Found In Dogs & Cats
1. Unusual lumps and bumps
One of the most commonly noticed signs that leads owners to seek veterinary care is the presence of new lumps or swollen lymph nodes. Lymphoma, a cancer of the lymphatic system, causes enlargement of lymph nodes that can be felt under the jaw, behind the knees, and in other locations. These nodes can swell substantially and become quite noticeable.
In cats, lymphoma is often associated with infection by the feline leukemia virus (FeLV). Vaccination against FeLV reduces the risk of infection and the related cancers, so discuss vaccination status and preventive care with your veterinarian.
2. Visible sores or skin changes
Skin lesions, persistent sores, or masses on the skin can indicate mast cell tumors or other forms of skin cancer. Because skin problems can also be caused by allergies, infections, or parasites, it’s important not to assume the worst—but do have any unusual or non-healing sores evaluated. A veterinary assessment, which may include cytology, biopsy, or other tests, will determine whether a lesion is cancerous and guide treatment planning.
3. Unusual bleeding or discharge
Bleeding from the nose, mouth, eyes, or in the urine, as well as persistent or abnormal discharges, can be a sign of disease including cancer. Oral tumors, nasal tumors, and cancers affecting internal organs can present with bleeding or foul odors. If you notice unexplained bleeding, bad breath that does not respond to dental care, or any abnormal discharge, seek veterinary evaluation promptly.
Other red flags include unexplained weight loss, a sudden change in energy or temperament—from playful and active to lethargic—difficulty eating or swallowing, coughing, persistent vomiting or diarrhea, and disturbances in bathroom habits. Any ongoing change in your pet’s normal routine or condition warrants attention.
Dog & Cat Cancer Prevention Tips
While not all cancers can be prevented, maintaining your pet’s overall health reduces risks and helps with early detection. Key prevention and wellness steps include:
- Regular wellness exams: Routine veterinary check-ups allow your veterinarian to detect subtle signs of illness early. For senior pets, more frequent visits—often twice a year—are commonly recommended so that changes can be identified quickly.
- Balanced, high-quality nutrition: Feed a complete and balanced diet appropriate for your pet’s age, size, and health needs. A diet that includes anti-inflammatory components—such as omega-3 fatty acids from fish like salmon and antioxidant-rich fruits—can support overall health. Discuss specific dietary needs with your veterinarian rather than relying on general advice.
- Healthy weight and exercise: Keeping your pet at a healthy weight through portion control and regular physical activity supports the immune system and reduces the risk of many chronic conditions.
- Vaccination and parasite control: Vaccines that prevent viral infections like feline leukemia help reduce cancer risk in cats. Effective parasite control and avoidance of known environmental toxins are also important.
- Dental and skin care: Good oral hygiene and prompt treatment of skin issues reduce chronic inflammation, which can contribute to disease. Regularly check your pet’s teeth, gums, skin, and coat and report concerns to your vet.
Early detection is one of the most powerful tools against cancer in pets. If you find a new lump, notice a persistent sore, observe unusual bleeding, or see any other unusual symptom, make an appointment for a veterinary evaluation. Diagnostic tests such as blood work, imaging (X-rays or ultrasound), and biopsy or cytology can establish a diagnosis and guide treatment options.
Keeping detailed notes—when symptoms began, how they have changed, and any other relevant observations—helps your veterinarian make timely and accurate decisions. Partnering with your veterinary team and staying proactive about preventive care and regular check-ups will give your dog or cat the best chance for early detection and effective treatment.