Cancer - One Word, Different Diseases

09/08/2016 15:00


But when talking about cancer, it's easy to forget that it's not one single disease. In fact, it's a range of different diseases, each of which has a different outlook and different treatment options.

Canine cancer

Cancer develops when a cell becomes faulty and grows out of control. And because virtually any type of cell in a dog's body can become faulty, this means there are almost as many types of cancer as there are cells.

In dogs, this equates to there being over 200 different types of cancer. In humans, it is likely to be a similar amount.

As with humans, cancer in general is more common among older dogs. But some cancers in particular are more common in dogs than others.

For example, lymphoma accounts for around 20% of all canine cancers, while hemangiosarcoma (a tumour that develops from endothelial cells, the cells that line blood vessels) is a common cancer in middle-age and older dogs.

Mammary carcinoma, a type of cancer that affects the mammary glands, is one of the most common cancers seen in unspayed female dogs. And osteosarcoma, a cancer of the bone, is also frequently seen among dogs.

Other common canine cancers include transitional cell carcinoma, mast cell tumours, melanoma, squamous cell carcinoma, soft tissue sarcoma and apocrine gland (anal sac) carcinoma.

Each of these types of cancer arise because of different genetic mistakes (also called mutations) developing in different types of cells.

Mammary carcinoma will develop because a dog's mammary cells have acquired certain genetic faults, while lymphoma develops because of faults in cells of your dog's immune system.

Different cancers and different breeds

While we know that cancer can and does affect all dogs, we also know that as well as there being different types of canine cancers, some breeds of dog are more likely to develop the disease than others.

For example, Rottweilers are known to be more susceptible to developing osteosarcomas, mast cell tumours and soft tissue sarcomas among other cancers, while Golden Retrievers are more prone to developing lymphoma.

Melanoma, which arises from pigment-producing melanocyte cells is common in Scottish terriers and Giant Schnauzers among others, while West Highland Terriers can be at a higher risk of developing bladder cancer.

The fact that different breeds of dog are more susceptible to some cancers than others highlights the fact that there's a huge genetic component to cancer in canines.

As in humans, mistakes in specific genes are associated with specific cancers - for example mistakes in the p53, PTEN or RB1 gene are known to increase a dog's risk of developing osteosarcoma. Mistakes in p53 along with faults in the p21 and p16 genes are thought to be involved in the development of melanoma in dogs.

Studies that determine which breeds of dogs are susceptible to cancer are important. But it's important to remember that they should be taken more as indicators of breed susceptibility rather than definitive conclusions.

This is because they are population-based studies which look at a certain population of dogs in a certain place, meaning the results and conclusions that they make depend on the prevalence of a particular breed within a given population.

Where in the world a study was carried out is also important because of differences in population. So a study done in the US may not be directly relevant in the UK.

Another important factor to be considered in breed susceptibility is underlying breed-associated health problems and inherited disease. For example, bulldogs appear to have a lower risk of developing cancer, but this could in fact be because as a breed, it has other health issues that contribute to it having a lower life-expectancy.

Early diagnosis

Even though these cancers all develop from different cells in a dog's body, and are characterised by different genetic faults, they have some things in common.

One of these is the fact that if they are diagnosed in the early stages they will be easier to treat, and treatment is more likely to be successful.

That's why it's important to be aware of some of the more commons signs and symptoms of cancer. These include

  • loss of appetite
  • weight loss
  • changes in behaviour
  • vomiting and diarrhoea
  • unusual odours
  • lumps and bumps under the skin

This is by no means an exhaustive list. So it's important to remember that if you notice anything unusual in your dog's behaviour or health you should bring them to your vet.

It will most likely be nothing, but it's better to get it checked out.

Treatment options

So if cancer isn't one single disease, but rather a range of diseases, what does this mean for treatment?

On the one hand it means that there's no single cure for cancer, no magic bullet that can be used to treat all of the different disease types.

This might sound disheartening, but it shouldn't.

The fact that we know there are different types of cancer that behave differently means vets can offer dogs the best, most appropriate treatment for them and their cancer.

By knowing the enemy we're dealing with we can better equip ourselves to fight it. And this in turn increases the likelihood of the treatment being successful.

Treatment will be tailored to a specific type of cancer, and will work to target the known weaknesses of a particular type of cancer.

The treatment options available to dogs are similar to those available to people. Surgery tends to be the most common type of treatment for canine cancers, with vets often recommending this to be followed by other treatments like chemotherapy or radiotherapy.

These last two types of treatment in particular can be tailored depending on the type of cancer, where in the body it is and what stage it's at.

Different combinations of chemotherapy drugs are used to treatment different cancers, often with good success. And radiotherapy is given in different ways using different doses depending on the tumour type and location.

We're also beginning to see more research into using immunotherapies to treat dogs with certain kinds of cancer.

This type of treatment, which is showing a lot of promise in human cancers, stimulates the body's own immune system to kill cancer cells. It's still early days for this treatment in the dog world, but it is certainly an area worth keeping an eye on.

Take heart

Understanding that cancer is a range of different diseases rather than one single disease is what's led to improved treatment and outcome for dogs with cancer.

Knowing the differences between different types of cancers allows vets to provide the most appropriate treatment for any dog that is sadly diagnosed with cancer.

It's also the reason that roughly 60% of dogs diagnosed with cancer will survive their disease. And with continued research into how to diagnose cancer early and new treatment options, let's hope that the statistics continue to improve.

That's something to look forward to.

Kristina is certified in Advanced Canine Nutrition.

