Cancer in dogs: your essential guide to the signs, treatment and care

Get the facts about cancer in dogs, including symptoms, possible causes and treatments, with advice from the Petplan veterinary expert.

Just like us, sadly many dogs will develop cancer as they get older. Around half of all dogs over the age of 10 will suffer from some type of cancer, and one in four will eventually die from the disease.

But while a cancer diagnosis in dogs is very upsetting, it doesn’t mean there is no hope left for your pet. In recent times, there have been huge advances in dog cancer care, meaning effective treatments are available – and an early diagnosis can be life-saving. And whatever the long-term outlook, there is plenty that you can do to care for a dog with cancer and ensure their quality of life, for as long as you have together.

Cancer is a disease caused by a collection of abnormal cells in the body growing and dividing uncontrollably, which form growths or lumps called tumours. Not all tumours are cancerous – those that stay where they originated are known as ‘benign’, and are much easier to treat.

Cancerous tumours, however, are often described as ‘malignant’ – they disrupt the normal functioning of the body and its organs, and can spread to other parts of the body. These cancer cells can break away from the primary tumour and travel through the body’s bloodstream or lymphatic system, creating new tumours in a process known as metastasis.

Due to the many different types of cancer found in dogs and the various bodily locations in which they can occur, there’s no definitive checklist of symptoms. However, if you notice a lump or growth on, or under, your dog’s skin, get it checked by your vet as soon as possible.

You should also keep an eye out for sores that don’t heal, chronic weight loss, a change in appetite, a persistent cough, lameness or stiffness, excessively smelly breath, lethargy, frequent vomiting or diarrhoea, bleeding from any bodily opening, and difficulties with eating, swallowing, breathing or going to the toilet. Any of these conditions could be symptoms of cancer in dogs – or of other health issues that require veterinary attention. And while some changes in older dogs are to be expected, if you’re worried about any out-of-character health or behaviour issues, it’s always worth getting them investigated by your vet.

Skin cancer

Skin cancer is the most common form of the disease in dogs, with three main types occurring. Mast cell tumours are the most widespread canine skin cancer, often found in Boxers and Pugs, and develop on the trunk of the body or the legs. Malignant melanomas tend to occur in the mouth, lips, toenail beds or pads of the feet, which can become infected. Sometimes misdiagnosed, these melanomas can grow fast and may spread to other organs. Squamous cell carcinomas may have a wart-like appearance and are regularly found in dogs with light skin or short coats, as they can be caused by sun exposure (also a risk factor for other skin cancers).


This type of cancer develops in cells found in the lymph nodes or internal organs, such as the liver, kidneys, spleen and digestive tract. Without treatment, an affected dog’s life expectancy may only be a couple of months or less, but with treatment it could be longer.

Mammary cancer

Early detection of mammary cancer in dogs is important, as tumours can advance quickly. However, female dogs that are neutered before experiencing their first reproductive cycle only have a 0.5% chance of developing mammary cancer. This increases to 8% if they are neutered after one cycle, and 26% after two cycles.

Bone cancer

This is most commonly seen in large breeds, such as the Greyhound, Saint Bernard and Mastiff. There are four main types of bone cancer in dogs, the most common of which is osteosarcoma, an aggressive and fast-developing form that tends to occur in dogs’ leg bones, or sometimes in the skull, spine or rib cage. Chondrosarcomas occur in cartilage joints, fibrosarcomas begin in fibrous connective tissues and synovial cell carcinomas come from joint tissues – all of which then invade the closest bones.

Mouth cancer

Usually seen in older dogs, oral tumours can cause loss of appetite, foul-smelling breath, drooling and difficulty eating.

Taking your dog to the vet is always the first step to getting answers about their condition. Bear in mind, however, that your vet can’t always determine the nature of an unusual growth simply by feeling it. So an initial examination may be followed by a fine needle aspiration (sucking some cells from the growth using a hypodermic needle and syringe), blood tests, an X-ray or ultrasound to identify the location and spread of any tumour, or a wedge-biopsy (surgical removal of a tiny piece of affected tissue) for further examination. CT or MRI scans also are becoming more widely available for pets, particularly for suspected brain tumours.

If your dog is diagnosed with cancer, it’s only natural to wonder what caused it, and whether there was anything you could have done to prevent it. As with cancers in humans, however, there is often no obvious underlying cause.

There may be a genetic component to some cancers in dogs, as certain breeds are more likely to develop the disease than others, including Golden Retrievers, Boxers, Bernese Mountain Dogs, and flat-coated Retrievers. Lifestyle and environmental factors that can trigger abnormalities in cells may also have a part to play. These could include exposure to chemicals, tobacco smoke, pollution or sunlight, lack of exercise, or poor nutrition. Making sure your dog stays active and eats a healthy diet is the best way to protect their long-term health.

As with humans, surgery, chemotherapy and radiation therapy can all be useful cancer treatments for dogs. In some cases, treatment may leave your pet cancer-free, while in other cases, it may simply improve their quality of life in the time they have left. The exact course of treatment offered by your vet will depend on the type and location of the tumour, whether it has spread, and what’s best for your dog.

Surgery can be an effective treatment option for cancer in dogs, especially those with skin cancers. With mammary cancer, surgery may be followed by chemotherapy to stop cancerous cells spreading. Chemotherapy drugs interfere with the ability of abnormal cells to divide, but they can also cause side effects, such as a compromised immune system or nausea.

It’s only natural to worry about putting your dog through chemotherapy, but dogs generally tolerate the treatment very well, and fewer than one in five will experience side effects. Breeds with continuously growing coats, such as Poodles, may experience some hair thinning, but dogs having chemotherapy don’t usually suffer fur loss.

Another treatment your vet may suggest is radiation therapy, which involves directing a beam of radiation to kill cancer cells – usually under a brief general anaesthetic, so your dog doesn’t move around. Recently there have also been huge advances in immunotherapy, where an animal’s immune system is stimulated to destroy the cancer. This treatment is gradually becoming more widely available, and there is a new vaccine against oral melanomas for dogs.

Every dog is different, and the care and attention they require will depend on the type of cancer they are fighting, their individual personality, the treatment they are receiving and the stage of treatment they’re at. Your vet will be able to advise you on your dog’s progress and how best to support them, including pain relief, how much activity they need, and what you can do to keep them happy and comfortable at home. As a general rule, try to take your cue from your dog – don’t fuss over them if they want to rest, for example.

If the prognosis isn’t good and your dog’s quality of life is seriously declining, your vet will also be able to guide you on end-of-life care. But with early detection, prompt treatment and loving attention, your dog stands the best possible chance of beating cancer or delaying the progress of the disease, so you can make the most of every day together.

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