Cancer in dogs
Just like people, dogs can get cancer, especially as they get older.
As with people, dogs often get cancer, especially as they get older. By far the most common areas affected are the skin and the breast, which is the most common in bitches.
What is cancer in dogs?
Cancer is the abnormal growth of a group of cells. They grow and multiply quickly, which can damage the surrounding tissue. Cancer can form a tumour (also known as a growth), which can spread to other parts of your dog's body.
Is my dog's tumour cancerous?
The language surrounding cancer can be confusing. Tumours can be cancerous, or non-cancerous, depending on what they do within the body.
There are two types of tumour:
- A benign tumour - these do not spread within the body, but can cause problems by placing pressure on adjacent organs
- A malignant tumour - these are cancerous and can spread within the body
What are the types of cancer in dogs?
The most common types of cancer in dogs include:
Skin cancer is the growth of cancerous cells in the skin. It's most commonly caused by exposure to sunlight. But it can also be caused by damage to the skin (such as excessive licking), or a genetic predisposition.
If your vet suspects skin cancer, they may carry out a biopsy. Skin cancer can usually be treated with surgery to remove the tumour.
Breast tumours are lumps in the mammary glands (around your dog's nipples). This type of cancer is most common in female dogs, dogs over the age of seven, and dogs who have not been spayed.
Around half of breast tumours are benign, but the rest may be malignant. Surgery is the main method of treatment for breast cancer in dogs.
Leukaemia or lymphoma is a cancer affecting the white blood cells (called lymphocytes). These white blood cells circulate in lymphatic system, where the body screens for infections and other harmful substances that try to enter the system.
When lymphocytes become cancerous, they increase uncontrollably. They often sit in one place and multiply, causing the enlargement of lymph nodes. This can cause lumps in areas such as the throat, liver, spleen or bowel. The cancerous lymphocytes can also easily spread to other parts of the body through circulation in the blood.
Because lymphoma is usually widespread, surgery alone is not usually recommended. Without treatment the average life expectancy from diagnosis is around two months. But this can be prolonged with chemotherapy. Sadly, not all lymphomas respond successfully to treatment. Your vet will advise you on your dog's prognosis.
What causes cancer in dogs?
The cause of some cancers in dogs is usually unclear. But there are some things that appear to make cancer more likely. Statistically, some breeds are more at risk from certain types of cancer.
You can also reduce the risk of breast tumours in female dogs by spaying them before the age of two. Reducing exposure to sunlight can also help to reduce the risk of skin cancer in dogs.
Straightforward links with diet and lifestyle have not so far been fully researched in dogs.
What are the signs of cancer in dogs?
While not all lumps are cancerous, finding cancer early can give your dog a better chance of recovery. If you spot a lump, contact your vet.
Because cancer can appear in any part of your dog's body, the symptoms can be varied. Signs of cancer include:
- a lump on the surface of the skin
- a sore that won't heal
- loss of appetite
- weight loss
- lethargy and weakness
- difficulty in breathing
- limping
- digestive or tummy problems that don't go away
These signs can appear in other illnesses too, so it's a good idea to take your dog to the vet if you spot them. Even though cancers may be slow growing, they can sometimes cause sudden signs of illness.
How is cancer diagnosed?
If your vet suspects your dog may have cancer, they will usually run some tests. This can include blood samples and X-rays. Other tests include:
- an ultrasound or MRI scan. These can help to see whether the cancer has spread to other parts of the body (this process is called staging). A scan can also provide a picture of your dog's general health. This is helpful for deciding the right course of treatment.
- a biopsy (taking a small sample for examination under a microscope). This may help to identify the tumour and see if it is cancerous. Sometimes, biopsies do not always contain enough good quality material when examined under a microscope.
How is cancer in dogs treated?
Since there are many types of cancer in dogs, treatment can vary. Treatment is also available for non-cancerous lumps. There are three common types of treatment:
- Surgery
- Chemotherapy
- Radiotherapy
The treatment your dog receives depends on their health, the type of cancer, and how far it has spread. Your dog's quality of life is important and, sometimes, your vet may recommend euthanasia as the kindest option.
Surgery is often chosen for skin tumours, or for internal growths. Surgery can provide a cure, but if the lump is thought to be benign and not causing your dog any issues, it may not be necessary.
When a cancerous lump is removed during surgery, it may be tested to find out if it has spread. Removing a large internal growth can relieve the symptoms, but there may be a risk of it coming back.
Removing a lump in certain parts of the body (such as the brain) can be very difficult, or even impossible. This can be a costly specialist procedure, and may not be the kindest option for your dog.
Chemotherapy can be used for several types of cancer. Sadly, it does not usually cure the cancer. Instead, the aim is to slow the cancer down and reduce the symptoms. Chemotherapy is sometimes combined with surgery.
If your dog needs chemotherapy, regular vet visits will be required. It is costly and can be stressful for your dog.
Radiotherapy is only available at a few specialist centres. It does not usually cure the cancer, and regular visits are often needed for a period of time. Because your dog needs to be absolutely still for the treatment, a short general anaesthetic is given for each treatment.
Radiotherapy is an expensive treatment option, and extra vet visits can be stressful for your dog.
Is it fair to treat a dog with cancer?
Vets understand the importance of keeping animals pain-free, and share concerns about the potential stress of some treatments. But most vets would agree that a healthy, happy dog does not need to be euthanised, even if they have an incurable disease.
Current painkillers for dogs are very effective. But, sadly, for all animals with an incurable cancer, there will eventually come a point when they are suffering and have lost their quality of life. You and your vet will work together to recognise when euthanasia is the kindest option for your dog.
Signs your dog is struggling or is in pain
- Changes in behaviour (such as being irritable or anxious)
- Loss of appetite
- Reluctance to move around and go for walks
- Restlessness or difficulty in getting comfortable
- An improvement in their behaviour with painkillers
If your dog is diagnosed with cancer, it's important to monitor them for signs of pain or suffering. While some medications can help relieve symptoms, there may be a time when they're no longer effective enough. Talk to your vet if you think your dog is struggling.
What is the prognosis for cancer in dogs?
The prognosis for dogs with cancer varies. It depends on the type of cancer and how far it has advanced. For some cancers there are specialised tests that can provide a clearer prognosis. But, like all illnesses, cancer can be unpredictable. Sadly, your dog's condition may suddenly deteriorate.
Note
We know that dealing with cancer can be difficult. You can find free, confidential support via our Pet Loss Support service. Help is available on the phone, webchat, email and a Facebook group.
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Reviewed
• 13 October 2025
Next review
• 13 October 2028
