Cancer in Dogs - Healthy Dog Food

In this article, James Hill MA Vet MB MRCVS talks through what cancer is, how it can affect our pets, signs to look out for, diagnosis and potential treatment available.

BACKGROUND

Our pets’ bodies (just like ours) are made up of many different cells which have specific roles to play to make up the different parts. For example skin cells have a different job to lung cells, or blood cells, or intestine cells, or brain cells etc etc.

The cells are controlled by code in genetic material called DNA in the nucleus in the centre of the cell. This DNA coding is held in the form of genes (hence “genetic code”). The DNA code is the same in all cells (except sperm and eggs) but different genes are expressed, or controlled, to give each cell type its different characteristics and function. For example a skin cell is controlled by the skin cell genes and the others, although present, are not used or “switched off”.

So cells are controlled by their genetic code which determines what sort of cell they are, what their job is, whether they need to divide or not, and, importantly how long they are designed to live before dying and being replaced.

SO WHAT IS CANCER ?

This genetic control of cells is incredibly complex and can go wrong in many ways. Small errors in the coding can be corrected, but sometimes a series of errors occurs that changes the nature of a particular cell so that it no longer behaves normally, fails to do its job and may grow out of control and even spread through parts of the body where it should not be. Such cells can carry on dividing without stopping, and may not die at the normal rate they were originally intended to.

This means that cancer can occur in any of the many, many cell types that make up the body. If it is one of the types of skin cell then a form of skin cancer will develop; if it is a gut cell then a form of intestinal cancer will develop etc etc

WHAT IS THE DIFFERENCE BETWEEN MALIGNANT AND BENIGN CANCER ?

In general a benign cancer only grows locally where its parent cell type “went wrong”, usually slowly and not aggressively invasive. A skin wart is an example of a benign cancer.

On the other hand a malignant cancer cell type will grow aggressively, sometimes quickly invading healthy neighbouring tissues, or spreading through the body by the bloodstream or the tissue fluid drainage (lymphatic) system. Malignant cancers damage the body in many ways, not just their increasing physical presence, affecting the function of various parts of the body and eventually causing the body to die.

WHAT CAUSES CELLS TO BECOME CANCEROUS ?

Many factors have been identified and research is on-going. Sometimes the genetic fault is inherited (ie passed on from the parents) but there are plenty of other contributing causes including viruses, toxins, radiation (including UV sunlight), pollution, diet, lifestyle, environmental and physical factors etc etc. It is impossible in most cases to blame one thing, and usually a number of genetic errors need to occur in a cell type to cause it to transform to cancer in the unlucky individual. There is no doubt, however, that an animal’s original genetic code (it gets half from each parent) plays a role in how susceptible an individual might be to cancer.

HOW CAN I SPOT THE SIGNS OF CANCER IN MY PET ?

Ideally you should get your pet checked over twice a year by your vet. This is often at the same time as vaccination and other routine preventative measures (eg worming, flea control etc) but it is an opportunity for you to raise ANY other health concerns you might have.

Some cancers are easily spotted – eg skin growths, gum growths, mammary growths etc. This is because they occur in parts of the body that are visible from the outside. Internal cancers, however, cannot be seen but will begin to affect the part of the body they originated in and, therefore, that body function. They may spread and affect other body functions too. So, for example, an intestinal cancer might affect digestion and cause diarrhoea and/or vomiting initially, but if it spreads then you might see weight loss and liver problems if it spreads to that organ, or lung problems (eg coughing or shortness of breath) if it spreads there (and so on).

This means that you need to watch for any long term changes in the normal state of your pet, including weight (loss), appetite, drinking, motions, urination, mobility, breathing, exercise tolerance, general demeanour and behaviour etc. Essentially anything out of the ordinary that does not go away, progresses or repeatedly comes and goes, should be reported to your vet so that the cause can be determined (remember there are many other diseases and health problems that are NOT cancer so do not panic and jump to conclusions, but let your vet find out).

ARE THERE SIMPLE TESTS MY VET CAN DO TO DIAGNOSE CANCER ?

Because there are so many different types of cancer some are more easily diagnosed than others. A visible skin growth could have many different cell type origins and behave in different ways, but it can be biopsied (removed or a piece removed surgically, or a few cells examined) and sent for laboratory analysis. This allows the vet to know which cell type is involved, how invasive it is, and how it is likely to behave. Obviously this will guide the treatment options and give an idea of prognosis (ie how the situation is likely to progress or not). Many cancers / tumours are not visible from the outside though and more involved testing may be needed to rule out other causes of the signs. Tests can include blood sampling to look at cells (red and white blood cells etc) and organ function (liver, kidney etc) as well some other more specific tests, but remember that there is no simple screen test for cancer in most cases. Other procedures might include imaging tests such as radiography (“X raying”), ultrasound, endoscopy and advanced techniques such as MRI and CT scanning (your vet may refer you to a cancer specialist [or oncologist] for these more involved procedures). Sometimes biopsies of internal tissues inside the body are taken (surgically or via endoscope), which can be very involved. Other samples such as urine or faeces can be tested too if needed.

So sometimes diagnosis is straightforward and quick, but very often life is not like that and a series of tests over time may be needed to get to the root of the problem (particularly if the early signs are vague and slow developing). Good communication and trust in your vet is essential for the best outcome.

WHAT CAN MY VET DO IF CANCER IS DIAGNOSED ?

There are many treatment options available. Some work well with one type of cancer and not with another (due to different cell types and behaviour) and often a combination approach is used (including general health support of the rest of the body). Some cancers are very difficult to treat, unfortunately.

Options include surgical removal (there are many techniques) – sometimes they are “de-bulked” but ideally the whole tumour is excised (this can have a good outcome if the tumour has not spread anywhere else). Obviously it is easier to remove a small skin mass than a brain tumour, so the site and size of the cancer plays a big part in decision making. Chemotherapy is the use of one or more drugs to target the cancer. The problem is that the cancer cells are still part of the body and so we need medicines that will preferentially kill tumour cells and not the body they live in. Drugs often target fast growing cells because that is what the cancer cells are doing, but there are other fast growing cells in the body which can become the innocent victims of the drug(s) [eg gut lining cells, hair follicles] leading to the side effects of chemotherapy. Such side effects can be serious and debilitating and need their own medical management, therefore having quite a negative effect on quality of life, which adds complexity to decision making for your pet.

Other options include radiotherapy for certain tumours/cancers (again it does not suit all types). This is mostly a referral procedure done by an oncologist, and involves the targeted overdose of a tumour with radiation to kill it whilst trying not to damage the surrounding tissues.

Overall your vet will help you decide which options can be tailored to your pet’s individual circumstances, which include many factors, not just the type and extent (how far it has spread) of the cancer. The background health and age of your pet play a role but there are also financial considerations as some of these procedures are inherently expensive (pet insurance can be a real help here). A careful on-going assessment of the pet’s quality of life between vet and owner is essential in advanced or serious cases.

WHAT IS MEANT BY PROGNOSIS ? HOW LONG HAS MY PET GOT ?

It is very tempting to ask your vet how long has your pet got with a particular cancer. Some types are curable, making the prognosis “excellent”, but other situations might carry a “good”, “fair”, “poor” or even “hopeless” prognosis. A vet cannot give an exact answer and will be reluctant to give any more than the most general prediction (which may be based on researched averages of how long animals have lived with certain cancer types at certain stages and given certain treatment regimes). These so called “median survival times” are impossible to apply accurately to individual cases, so it is better to review the case frequently with your vet and see where you are at each point in time rather than pinning hopes on what is little more than an educated guess.

OVERALL

This is a huge topic to cover and I have only skimmed over the basics to give you some background. It is important to involve your vet at as early a stage as possible if you have any such health concerns. Early diagnosis and treatment generally carry a much better prognosis – good for both your pet and you. Obviously a good lifestyle is as important for your pet as it is for us, so a good diet, plenty of exercise, avoiding obesity, routine preventative health care (vaccines, parasite control, health checks) and generally avoiding risk factors are key to reducing the likelihood of cancer.