Nobody wants to think about the “C-word,” but unfortunately, cancer is a leading cause of death among dogs. According to veterinary oncologist Dave Ruslander, 50% of dogs over age 10 will develop a type of cancer, which makes being aware of dog cancer signs and symptoms important as your best friend gets older.
What is dog cancer?
As the body ages, its disease-fighting immune system weakens, and it becomes more vulnerable to disease. It’s important, therefore, to learn the early signs of cancer and the different types of canine cancer to keep your dog as healthy as possible for as long as possible—in addition to providing a wholesome diet, age-appropriate exercise, and mental stimulation.
If you do suspect a problem, consult your vet to learn about treatment options. We also highly recommend the Dog Cancer Survival Guide, written by veterinary experts, to help you make the best decisions for your dog’s care.
Keep in mind—early detection is key to optimising your dog’s options for successful cancer treatment and improving their overall quality of life. 
Signs your dog may have cancer
Just like in humans, there is no one symptom that points to cancer. It can be an elusive early diagnosis, so being educated on possible symptoms is key. Dave Ruslander also has stated while dogs over 10 have a higher risk of developing cancer, 50% of those cancers can be treated if caught early.
Some of the most common signs of dog cancer are:
- Tumours and unusual growths
- Unnatural swelling in tissue and bones
- Swollen lymph nodes
- Abnormal bleeding
- Lameness
- Wounds that won’t heal
- Sudden unexplained weight loss or gain
- Lethargy
- Difficulty breathing
- Difficulty going to the bathroom and/or unusual poop
Here are some ways you can identify these symptoms in your dog. As always, if you are concerned about any new symptoms, it’s best to contact your vet right away.
Tumours, mysterious swellings, and unusual growths
Although it’s probably the first symptom that comes to mind when you think about cancer in dogs, tumours are not always cancerous. As dogs age, they’re more likely to develop fatty deposits and other benign lumps.
But some growths can be malignant, and tumours can signal skin cancer, mammary cancer, and other types of cancer. Skin tumours are one of the most common types of growths your dog could develop, so be on the lookout for these.
Swollen lymph nodes are another thing to watch for. These lumps don’t cause pain, but they can indicate lymphoma—one of the most common types of cancer in dogs, particularly in Golden Retrievers. Swollen lymph nodes could also signal leukaemia or a different type of cancer that has metastasised (or spread), causing inflammation of the lymph nodes.
You can perform a monthly “lump check” to keep track of your dog’s lumps and bumps. This is especially important for older dogs who develop benign growths all the time.
With practice, you can learn how to tell the difference between a benign fatty deposit and a more concerning growth. But if a new lump or swelling develops, it’s a good idea to check with your vet just in case.
Wounds that won’t heal
Like tumours, persistent wounds can be signs of cancer in dogs. Typically, a small wound or lesion should heal over time, with visible signs of healing (i.e. scabbing and skin and hair regrowth). If your pet has a recurring lesion or wound that just won’t heal, it’s time to see the vet to rule out cancer or another serious health issue.
Red, irritated lesions could indicate mast cell tumours, one of the most common skin tumours found in dogs. Though more commonly found on the skin, MCTs can also spread to bone marrow or other organs.
Sudden lameness
“Lameness” is a change in your dog’s regular gait. It may present as tenderness and subtle pain, limping or favouring a limb, or in severe cases, the inability to place any weight on the limb. Basically, lameness = pain, and it can be an indication of bone cancer, particularly in older dogs.
You don’t need to panic about every little hitch in your dog’s step (particularly if they’re an older dog with arthritis), but sudden, persistent lameness should be evaluated by a vet.
Rapid, unexplained weight loss or gain
Weight loss is a particularly common sign of cancer in dogs and may indicate a gastrointestinal tumour that’s otherwise undetectable from the outside. If your dog starts losing weight rapidly, whether their appetite changes or stays the same, get to the vet ASAP.
Sudden weight gain or bloating can also be a sign of canine cancer. If your dog maintains their regular appetite but seems to gain weight quickly, it’s time for a check-up.
Abnormal discharge or bleeding
Abnormal discharge or bleeding anywhere on the body is cause for concern, but this dog cancer symptom is most visible on the face. Funky eye discharge or a sudden bloody nose can indicate certain types of canine cancer, such as eye and skin cancers.
Similarly, sores and bleeding in the mouth can be a sign of oral tumours, which often go undetected because people assume the discharge and odour is a normal sign of ageing. While bad breath is common in older dogs, unusual odour, discharge, or bleeding is cause for concern.
Lethargy
Old dogs slow down. It’s an unfortunate but unavoidable fact of doggy life. However, a sudden, unexplained lack of energy—lethargy—can be a sign of illness or disease.
Lethargy is different from plain old tiredness in that it alters your dog’s enthusiasm level. They may suddenly lose interest in a favourite toy or activity, or fail to get up and greet you when you come home from work. Other signs of lethargy may include excessive sleep and delayed responses to visual and auditory stimuli.
Lethargy is a general symptom of a broad range of issues, so it doesn’t automatically signal cancer. But if your dog is suddenly a lot less active than usual, something could be going on.
Unusual poop
You know your dog, and you see her “output” every day. You probably have a sense of the difference between normal poop, somebody-got-into-the-cat-food-again poop, and something more concerning. Persistent diarrhea, hardened stools, and straining can all be symptoms of cancer in dogs.
If you’re concerned about something in your dog’s output, don’t hesitate to call the vet. In particular, watch for black, tarry stools, which can indicate ulcers, a symptom of mast cell tumours.
Difficulty breathing or going to the bathroom
One of the most common (and alarming) signs of illness or injury is when normal bodily functions become laboured or painful.
If your dog is having trouble breathing, straining to go to the bathroom, or otherwise seems uncomfortable during normal activities, don’t hesitate to have her checked out. Sudden, extreme discomfort or pain are important warning signs that shouldn’t be ignored.
Most common types of dog cancer
Research shows that the most common types of dog cancer in the UK are:
- Cutaneous histiocytoma (skin cancer)
- Adenoma
- Soft tissue sarcomas
- Mast cell tumour
- Lymphomas
While some of these cancers are incurable, current treatment options could extend your dog’s life while keeping them comfortable.
Others are curable, and early intervention is key.
You don’t have to fear dog cancer
Cancer is scary, but you don’t have to live in fear of it. Remember: modern dogs live a lot longer than their ancestors did. The fact that dogs routinely live beyond the age of ten is a great indication of how far pet care and veterinary medicine have advanced.
The good news—canine cancer treatments have improved significantly, and pet owners now have the option to pursue treatments like surgery, chemotherapy, and radiation therapy. Knowing these early dog cancer signs could help get your dog treatment faster.
So track your dog’s health, and see the vet if you or your dog sitter notice something unusual. The rest of the time, continue enjoying life to the fullest with your four-legged best friend.
