Cancers are common in older pets



The lump on 12 year old Marnie’s back is a rare, very fast growing tumour called a myxoma. It was removed a few days after this picture was taken.

Cancers will never be completely prevented for the simplest of reasons. Cancers are nothing more than distorted versions of normal cells. Our dogs and cats, and you and I are all genetically predisposed – if we live long enough – to potentially develop cancers. That’s what I mean when I say cancers are ‘normal’.

I first used chemotherapy in 1979 on the then American ambassador Kingman Brewster’s Labrador. The dog had a form of leukemia and I had read that the pharmaceutical company Upjohn, in Michigan, had a licenced, injectable treatment that might be effective. It took one ton of blue periwinkles to make a single injection so the drug was very costly. The embassy was able to help get the drug and the Brewster’s delightful black Lab went into ‘permanent remission’. (And after the Brewsters returned to Connecticut my wife and I became regular summer guests of Kingman and Mary-Louise at their New Haven home!)

A great advance in understanding cancer is the realisation that there are biological rules that govern the way normal cells transforms themselves into cancer cells. The oncologist Robert Weinberg says there are probably just six ‘rules’ that apply to all cancers. Paraphrasing him, they are:

  1. Cancer cells, by activating genes called oncogenes, have the ability to proliferate on their own – autonomously. These cancer cells are self-sufficient.
  2. Cancer cells suppress and inactivate the genes that help cells to naturally die. By doing so they avoid programmed death.
  3. Cancer cells activate specific genes that make them immortal. They are able to reproduce themselves forever and ever. They have a limitless ability to replicate themselves.
  4. Cancer cells inactivate tumour-suppressing genes. By doing so they are insensitive to growth-inhibiting signals and mechanisms.
  5. Cancer cells acquire the ability to grow their own blood vessels. They can supply themselves with nourishment.
  6. Cancer cells acquire the ability to migrate around the body, to invade and colonise organs and tissues far from where they originated.


Once medicine understands what the mutant genes are, it then needs to know how they function. That will lead to drugs than inhibit cancer growth without killing normal cells. (The first of these drugs have been developed for specific human cancers.) This understanding will improve cancer prevention.

As well as traditional epidemiology studies (for example those that associated smoking with lung cancer) epidemiology will integrate cancer screening with cancer genetics. As dog cancers are being used to study human cancers, there may be dramatic benefits for preventing cancers known to be prevalent in certain breeds. The greatest challenge is to understand how cancer cells behave. Won’t it be exciting when we learn exactly how a cancer cell become immortal?

Dogs and cats are living longer than ever and are better cared for now than at any time in their evolution. You may read that cancer in dogs and cats is increasing.  This is certainly true but it is the diagnosis that is increasing not necessarily the incidence. For example, until MRI brain scans became available, it was thought that brain tumours were rare in dogs. Diagnostics improved and now we know that brain tumours are not rare and in fact are more common in dogs than they are in people.

In the UK, one third of all dogs are over 10 years of age, one of the highest percentages in Europe. (In Greece for example less than 5% of dogs are over 10 years old.) An older population is simply more likely to develop cancers. We also have a high percentage of purebred individuals and unwittingly, in selecting for certain shapes, sizes or temperaments, for example breeds such as the Bernese Mountain Dog and Flat-coated Retriever, we have also genetically selected for increased risk of cancers.

At the London Vet Clinic we see cancers on a daily basis. If a cancer can be surgically removed and it’s in a pet’s interest to do so we remove it. If a cancer can’t be completely cured through surgery, but an individual will have a longer and more comfortable life as a result of surgery we discuss the pros and cons with you. Grant Petrie has been providing chemotherapy for pets at the London Vet Clinic for over 25 years. If drug treatment is useful Grant will talk to you about that. We will discuss the value of referral for radiation therapy, often useful to dramatically reduce cancer discomfort. The great difference between treating cancers in pets and in us is that we will not suggest a treatment if we think your pet will suffer from that treatment. A little short term discomfort following surgery, or thinning of the coat as a result of chemotherapy is acceptable but because our pets have no say in the matter we try to act as their voices, making decisions that are in their best interest.

If you want to talk about your pet’s health please telephone us on 02077232068 and book an appointment.

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