You may have noticed that your normally hungry pooch is suddenly off their food. Or perhaps your energetic kitty is now lethargic and reluctant to move. These symptoms might seem non-specific, but they can both be signs of cancer. Although we never want to think the worst, early detection is the best thing you can do for your pet. If you are concerned about any of the symptoms below, you should speak to your veterinarian.

Types of cancer

Cancer comes in many different forms and can affect nearly any part of the body, so symptoms will vary significantly based on the type and location. Some of the most common cancers in dogs include lymphoma (affecting the lymph nodes or bone marrow), hemangiosarcoma (affecting the blood vessels), mast cell tumors (found in skin and other tissue), melanoma (a type of skin cancer), osteosarcoma (bone cancer) and mammary cancer. Among cats, the most common cancers are lymphoma, fibrosarcoma (also known as soft-tissue sarcoma) and squamous cell carcinoma (a type of skin cancer).

Common signs of cancer

Abnormal lumps or swelling–this is a common sign, and vets recommend that any unusual lump under the skin should be removed and biopsied, particularly if they continue to grow.

Persistent sores – these are lesions on the skin that won’t heal even after treatment with ointment or antibiotics.

Abnormal discharge or bleeding – continued discharge from the eyes or nose, or bleeding from the nose is a common sign of eye or facial tumors.

Unusual or offensive odor – yes, we all know our pets' breath can get a bit smelly, but if you notice any changes or the odor becomes particularly bad, it could be a sign of mouth cancer.

Loss of appetite – there are a number of different cancers that can put your pet off their food, so keep an eye on any extras that are being left behind in their bowl.

Unexpected weight loss/gain – sudden weight loss that cannot be explained by diet or other illnesses may indicate a gastrointestinal tumor. Sudden weight gain or persistent bloating can also be a warning sign of cancer.

Lethargy or loss of stamina – if your usually-active pet suddenly loses energy, it’s a sign there’s something wrong. It might not be cancer, but a change in activity levels should always be checked out by a vet.

Sudden lameness or stiffness – dogs, in particular, are prone to exercise-related injuries, so don’t become paranoid about every slight limp, but sudden lameness or stiffness can be a sign of bone cancer.

Difficulty breathing, urinating or defecating– problems with any normal bodily functions can indicate pain caused by cancer, or can be more directly caused by a tumor directly impacting the area.

Diagnosing cancer

None of these symptoms alone can be used to definitely diagnose cancer. However, if you notice any of the above signs, you should have your pet checked out sooner rather than later, as early detection can be vital.

To confirm or rule out the presence of cancer, your vet will conduct a number of tests, depending on the signs and the part of the body. These can range from a simple physical exam to look at lumps or sores, to blood tests, urinalysis, x-rays, and ultrasounds. Once a diagnosis has been made, the veterinarian will speak to you about the best course of treatment.