Cancer in Dogs


As dogs get older, sometimes they can be affected by cancer, just like humans. Receiving a cancer diagnosis for your dog can be extremely worrying and difficult. However, there are treatments available that in many cases can help dogs to make a recovery. This blog takes you through the most common symptoms associated with cancer in dogs, as well as some of the techniques used to diagnose and treat it. We’ll also go through some of the most common types of cancer, and how to spot them.

Symptoms of Cancer in Dogs

The earlier the diagnosis, the better when it comes to treating cancer. If you notice anything that doesn’t seem quite right, it’s always best to make an appointment with your vet to get it checked out. While this isn’t an exhaustive list, some of the common symptoms of cancer in dogs include:

  • A lump on the body
  • Low energy and weakness
  • Reduced appetite
  • Weight loss
  • Limping
  • Drinking more
  • Vomiting
  • Digestive problems
  • Breathing difficulty
  • A sore that won’t heal

What to Do if Your Dog Has a Lump

It’s always best to get your dog checked by a vet if you notice a lump (or any of the other symptoms listed above).

If you find a lump or bump somewhere on your dog’s body, it can be very worrying. However, it’s important to remember that not all lumps will necessarily be cancerous. Lumps filled with fluid are called cysts, and are usually not cause for concern. Hard lumps, known as tumours, can either be benign (non-cancerous) or malignant (cancerous).

It’s not possible to know by simply looking at a lump whether or not it’s cancer.

Diagnosing Cancer in Dogs

There are two common tests that can be carried out to determine whether a lump is cancerous. These include:

Fine Needle Aspirate (FNA)

This is where a needle – similar in size to those used for vaccination – is used to take a sample of the cells from the lump. Since the needle is small, it is usually quick and painless, and can often be done during the consultation with your vet, depending on where the lump is on the body.

This method is ideal for identifying harmless fatty lumps. However results can be less predictable for firmer masses, sometimes resulting in negative or inconclusive results.

If the tests show that the mass is benign, like a fatty lump, treatment may not be necessary. Instead your vet can simply monitor the lump for any changes.

Tissue Biopsy

A tissue biopsy is a much more accurate way of testing a lump, almost always resulting in a diagnosis. However, it must be done with the dog under sedation or full anaethesia, which means that it carries with it a few more risks and is more expensive.

The procedure involves removing a representative part of the lump, and sending it to a specialist pathologist to examine. The pathologist will look at the type of cells present, but also how those cells are interacting with each other. As well as identifying the type of tumour, this technique can also tell us how the tumour is likely to behave. This is known as the tumour grade.

Tumour Staging

Often further testing will be recommended after the results of the FNA or biopsy before deciding on treatment for your dog. This is known as tumour staging. While the tumour grade tells us how aggressive the cancer is, tumour staging tells us if it has, or is likely to, spread to other parts of the body.

Cancer spreads when cancer cells leak into the blood or lymphatic system. There are specific areas of the body that cancer cells are more likely to spread to, so your vet will check these particular areas. They include the lymph nodes, lungs, liver and spleen. There are different methods used to check each body part, such as tissue sampling like those outlined above, as well as imaging methods such as X-rays, CT scans and ultrasounds.

Once your vet knows the tumour grade and tumour staging, they can predict if the tumour is likely to spread, and if so, where it may spread to. Your vet can then determine whether removing the lump through surgery is likely to cure your dog. Or, they may recommend that additional treatment like chemotherapy or radiotherapy is needed. Every case is different.

Chemotherapy for Dogs

Chemotherapy may be given after surgery, but it can also be used as a primary treatment for certain types of cancer in dogs.

Chemotherapy involves administering a type of drug that kills or harms cancer cells. This is most often given as an injection or infusion over the course of several treatments, typically every 2 to 4 weeks. Some pets might need sedation if they are very stressed or uncooperative as it’s important to administer it correctly.

Less commonly, chemotherapy drugs can be given at home in the form of tablets.

Your vet will be able to talk you through the different options available and advise you on the best choice for your dog.

Are There Side Effects of Chemotherapy for Dogs?

Chemotherapy for dogs involves lower doses than commonly given to people. This means that the drastic side effects seen in human chemotherapy are rare in dogs.

For example, complete hair loss is unlikely, though the coat may become a bit thinner. There are still some other side effects, such as vomiting, diarrhoea and increased risk of infection, but the most common ones are mild, and the more severe ones rare. All dogs are different though, and the side effects can be marked for some pets. Speak to your vet if you are concerned.

Types of Cancer in Dogs

As with humans, there are lots of different types of cancer that can affect dogs. Some breeds are more susceptible to certain forms of cancer than others. Symptoms and treatment plans will differ for each type of cancer in dogs.

Canine Lymphoma

Lymphoma is a common type of cancer in dogs, usually affecting middle aged dogs around 6-9 years old. It can affect any breed, but is seen more often in the following breeds:

  • Boxers
  • Bull mastiffs
  • Basset hounds
  • St Bernards
  • Scottish terriers
  • Airedale terriers
  • Bulldogs

Symptoms of Lymphoma in Dogs

The most common symptom of lymphoma in dogs is a painless swelling of the lymph nodes. The lymph nodes are located throughout the body, but they are most visible in dogs under the angle of the jaw, in front of the shoulders, and at the back of the knees.

Canine lymphoma usually just affects the lymph nodes, but can occasionally affect the gastrointestinal tract, the skin, inside the chest cavity, or other sites such as the heart or spine. Depending on the type of lymphoma, dogs may experience some of the following symptoms:

  • Lethargy
  • Loss of appetite
  • Weight loss
  • Increased thirst and urination
  • Muscle weakness
  • Vomiting and diarrhoea
  • Difficulty breathing

Having said this, many dogs will still feel well at the time of diagnosis.

Canine lymphoma is treated with chemotherapy, since it affects the whole body.

Breast Cancer in Dogs

Mammary or breast cancer is the most common form of cancer in female dogs. This type of cancer is thought to be linked to hormones; the risk of developing breast cancer can be significantly reduced by spaying your dog before their second season. Any breed can be affected and the average age for developing mammary tumours is 8 years.

Symptoms of Breast Cancer in Dogs

Generally, mammary tumours do not cause any symptoms, other than lumps. These usually start as small pea-sized lumps near to the nipple. You might not be able to see them as they form under the skin, but they can easily be felt. Sometimes multiple lumps may form in a line.

Mammary tumours are most often found when the dog is having their tummy rubbed, while being groomed, or during a routine examination.

If you do find a lump on your dog’s breasts, remember that around 50% of mammary tumours are benign (not aggressive). However, vets still usually recommend that all mammary growths are treated quickly as they can develop. See your vet as soon as possible if you notice any lumps.

The only reliable way to diagnose breast cancer in dogs is through a tissue biopsy, outlined earlier in this blog. It is common for mammary cancer to spread to other parts of the body, particularly to the lungs, so vets will usually examine the lungs prior to treatment as well, using X-rays or CT scans.

Skin Cancer in Dogs

The most common type of skin cancer in dogs are mast cell tumours. All mast cell tumours are considered malignant, but they vary a lot in how quickly they grow and spread. This kind of tumour typically occurs in middle aged dogs (around 8 years old). They can affect any breed, but it’s more prevalent in the following:

  • Boxers
  • Bulldogs
  • Boston terriers
  • Labradors
  • Golden retrievers

Symptoms of Skin Cancer in Dogs

Mast cell tumours can occur anywhere in the body, but they are most common on the torso followed by the legs. They can be within or on the skin, or sit underneath the skin. They often appear swollen, inflamed and have no fur on them. Mast cell tumours don’t all look the same though, so always check any new lumps with your vet.

The majority of mast cell tumours can be diagnosed using fine needle aspirate, described earlier in this blog. A biopsy is needed to find out the tumour grade (how the cells are behaving) and sometimes imaging and sampling of other parts of the body are carried out at the same time in case the tumour has spread (staging).

If the tumour hasn’t spread, removing it surgically is often curative.

Bone Cancer in Dogs

Nearly 85% of all bone tumours in cats and dogs are osteosarcoma (OSA), making it the most common form of bone cancer for our pets. The majority of cases are found in the legs, usually on the wrist, shoulder and knee. It can affect dogs of any age, but most commonly affects middle-aged and older dogs. It’s particularly prevalent in larger breeds such as:

  • Great danes
  • Dobermanns
  • German shepherds
  • Golden retrievers
  • Rottweilers

Symptoms of Bone Cancer in Dogs

Dogs may not show any signs of OSA in the early stages of the disease, but once big enough, the tumour will start to cause some pain. Dogs will start to limp on the affected leg. You might also be able to see some swelling in the affected leg compared with the other side. Occasionally dogs may suffer a broken leg as the bone becomes weakened by the tumour.

X-rays coupled with certain characteristic changes are often enough to make a diagnosis of this type of cancer in dogs. Sometimes a biopsy is also needed to be certain.

Unfortunately, this type of cancer is very aggressive and it is difficult to treat. Although amputation of the affected limb and chemotherapy can help dogs to live longer, it is unlikely to be curative. Many owners therefore feel that these treatments are not the right decision for their dog, and a number of pets are put to sleep soon after a diagnosis.

Wrapping Up

The different types of cancers discussed above are not exhaustive, but they are some of the more common ones. Other types of cancer often found in dogs include soft tissue sarcomas and oral tumours, while bladder tumours are much less common. In all cases, your vet will be able to talk you through the different treatment options, and help you understand the likely prognosis. If you spot any of the symptoms outlined in this blog, always see your vet as soon as possible. An early diagnosis will improve your dog’s chances of making a recovery.

For more information about conditions that affect older dogs as well as advice on diets and general care, head to Senior Dogs.

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