CANCER

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22/01/2018
CANCER With some humility, medicine realized – only in the last decade – that cancers will never be completely prevented because they are nothing more than distorted versions of normal cells. Our dogs and cats, and us, we are all genetically predisposed – if we live long enough – to potentially develop cancers. In that sense, cancers are ‘normal’.

Perhaps the greatest advance  in understanding cancer is the realization that there are rules that govern the transformation of normal cells into malignant cells. The oncologist Robert Weinberg suggests that there are probably just six ‘rules’ that apply to all cancers. Paraphrasing him, they are:

Cancer cells, by activating genes called oncogenes, have the ability to proliferate on their own – autonomously. They are self-sufficient.

Cancer cells suppress and inactivate the genes that enable cells to die. By doing so they avoid programmed death.

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.

Cancer cells inactivate tumour-suppressing genes. By doing so they are insensitive to growth-inhibiting signals and mechanisms.

Cancer cells acquire the ability to grow their own blood vessels. They can supply themselves with nourishment.

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 those drugs have been developed for specific human cancers.)

This understanding will improve cancer prevention. As well as traditional epidemiology studies (such as 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. Exactly how, for example, does 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 twice as common in dogs as 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 selection for certain shapes, sizes or temperaments in particular breeds such as Bernese Mountain Dogs and Flat-coated Retrievers we have also genetically selected for increased  risk of cancers.

At the London Veterinary Clinic we see cancers on a daily basis. If they need to be removed and it’s in a pet’s interest to do so we remove them. 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. If drug treatment is useful we’ll talk about that as we will discuss the value of referral for radiation therapy, often useful in dramatically reducing 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 with chemotherapy is acceptable but because our pets have no say in the matter we act or at least try to act as their voices, making decisions that are in their best interest.

For more information on cancers visit the medical pages.

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