Signs of Cancer in Dogs and Cats: When to See Your Veterinarian

What is cancer in pets?

Cancer develops when abnormal cells grow uncontrollably in the body. The rapidly dividing cells can form masses, affect organs, bones, blood, and skin, and even invade and damage surrounding tissues. They can also sometimes metastasize (i.e., spread) to other body areas. Cancer can affect any pet but is more commonly diagnosed in older animals. The causes of cancer in pets include genetic factors, environmental influences, and unknown triggers.

What are signs of cancer in pets?

Signs vary depending on the cancer type and location. Watch for these key signs:

Lumps and bumps in dogs and cats

One of the most noticeable signs of cancer in pets is the presence of lumps or bumps on their body. Regularly checking your pet during grooming or playtime for new lumps can help you catch issues early. Swollen lymph nodes, which may be associated with lymphoma in dogs, can feel like firm lumps under the jaw, in front of the shoulders, or behind the knees. While not all growths are cancerous, any new, unusual, or rapidly growing lump should be evaluated by a veterinarian.

Unexplained weight loss in pets

Unexplained weight loss in pets is always concerning and can indicate underlying health issues. Some cancers, including lymphoma or liver cancer in dogs, may present with weight loss, lethargy, or changes in appetite. When a pet loses weight with no change in diet or activity level, their body may be undergoing a metabolic shift caused by a tumor or cancerous cells. Cancer can cause weight loss by interfering with nutrient absorption or increasing the body’s metabolic demands. Cancer can also suppress a pet’s appetite because of pain, nausea, or other systemic effects. If your pet experiences unexplained weight loss, consult your veterinarian as soon as possible.

Changes in eating habits

Changes in eating habits, such as decreased appetite, difficulty eating, or an aversion to certain foods, can be a sign of cancer in pets. When a pet loses interest in food or struggles to eat, a tumor or other serious health issue affecting their mouth, throat, or digestive system may be the cause. For example, a pet may be reluctant to eat because of an oral tumor that causes pain, swelling, or difficulty chewing. Gastrointestinal (GI) tumors can cause nausea, vomiting, or changes in bowel movements that diminish appetite. Monitoring your pet’s eating habits and noting any changes can provide crucial information for your veterinarian.

Lethargy or decreased energy

A noticeable drop in energy, reluctance to play, or general lethargy can indicate your pet is not feeling well. Cancer can cause systemic fatigue and weakness, because the rapidly dividing cells or secondary issues, such as anemia, demand energy. If your pet seems unusually tired or avoids physical activity, have them checked by your veterinarian.

Persistent cough or breathing changes

A chronic cough or breathing changes, such as rapid or labored breathing, can point to respiratory or lung cancer. Pets with chest tumors may cough, wheeze, or struggle to breathe, and need immediate veterinary attention, because the signs could indicate advanced disease.

Non-healing wounds

Cancer can affect the immune system and skin, leading to sores or wounds that won’t heal, despite treatment. This is often seen in skin cancers, where malignant cells interfere with the normal healing process. Non-healing wounds are a potential cancer red flag and should be evaluated to rule out infection or other underlying conditions.

Changes in urination or defecation

Cancer, especially when the digestive or urinary tract is affected, can impact your pet’s bathroom habits. Signs may include difficulty urinating or defecating, changes in stool color or consistency, or blood in the urine or feces. These signs can be associated with bladder cancer, GI tumors, or prostate issues and your veterinarian can determine the cause.

Signs of pain or discomfort

Signs of discomfort can sometimes indicate cancer, particularly in the bones or joints. For example, bone cancer often causes noticeable limping because of pain. Your cat or dog may avoid certain activities, wince when touched, or display other signs of pain.

If you notice any of these signs, schedule a veterinary exam. Early evaluation allows your veterinarian to determine the cause and recommend appropriate next steps.. Contact your AAHA-accredited veterinarian today if you are concerned your pet may have cancer or they are due for their regular wellness visit.