Wednesday 23 October 2019

How science can help dogs and cats with cancer

Half of all flat coated retrievers die from hereditary cancer
Half of all flat coated retrievers die from hereditary cancer

Pete Wedderburn - Animal Doctor

Cancer is the biggest killer of dogs over the age of ten, with one in four dogs developing cancer. And it's common in cats too. Veterinary researchers have been working hard to find out how to prevent and treat this challenging issue.

Cancer research has four main areas of focus: diagnosis, prevention, treatment and palliative care.

Diagnosis generally involves taking a biopsy from a suspicious area and having it analysed by a laboratory: techniques for doing this are now easier, cheaper and less invasive.

Prevention is easy in theory: you need to know the cause, and then remove the cause. The challenge is that the cause is not always easy to identify. Broadly, cancer is caused by damage to DNA which then leads to uncontrolled division of abnormal cells. This damaged DNA can be inherited (breed-related) and or acquired.

Inherited cancers are common in some breeds of dog. Flat-Coated Retrievers, Golden Retrievers, Irish Wolfhounds and Labrador Retrievers are affected, with cancer dramatically shortening the average lifespan of some breeds e.g. over 50% of Flat-Coated Retrievers die of cancer, and the average age of this breed is only eight years. For researchers, identifying the specific genetic causes of inherited types of cancer is a key goal. If the specific genes linked to the cancers can be identified, these can be removed by screening the population before breeding from dogs, only breeding from those that do not have the offending gene. This is a very active area of current research.

Acquired cancer is more difficult to prevent: there's a long, long list of known and possible causes of cancer but there are some specific ones that pet owners should know about.

Ultraviolet radiation from sunlight causes malignant squamous cell carcinoma of the ear tips and nose of white cats, because they have no pigment to protect them from the sun. Regular application of sun block to white cats' ears and nose tips prevents this type of cancer.

Viruses can cause cancer and vaccines can sometimes protect against these, preventing specific cancers. Feline Leukaemia Virus, causing leukaemia in cats, is the best example in pets.

Hormones can have a strong effect on cancer. Repeated exposure of mammary tissue to high levels of oestrogen predisposes to cancer: if a bitch is spayed before her first season, the risk of cancer is reduced by 99.5%. In cats, spaying at any age reduces the risk of mammary tumors by 40% to 60%.

In contrast, early spay/neutering of giant breeds of dog is linked to an increased incidence of osteosarcoma (bone cancer), so it is now recommended to leave these breeds until sexual maturity before doing the operations (e.g. 18 months of age).

Nowadays, vets say that a decision on spay/neuter should be done on an individual basis, depending on the specifics of the pet, to optimise timing.

Chronic inflammation caused by some diseases can lead to cancer e.g. intestinal cancer in pets can follow long term inflammatory bowel disease in some cases. Prompt and effective treatment of such illnesses may reduce the risk of cancer

Finally, inhalation of tobacco smoke is linked to cancer in pets: many pets spend almost 24 hours a day in the house where chemicals and toxins can linger in the air or furniture. So if people stop smoking in their own homes, they reduce the risk of this type of cancer in their pet.

There are four main forms of treatment of cancer.

First, surgery: early excision of cancerous tissue, as well as a wide margin of normal tissue around it, is still the most effective way of treating many cancers.

Second, chemotherapy, with injections and oral medication, has been used for many years to treat cancer. Essentially, these are poisons that selectively act on cells that are dividing rapidly, and since in adult animals, cancer cells are often the main ones that are dividing rapidly, chemotherapy selectively acts on cancer cells. More recent types of chemotherapy include targetted cancer drugs, such as drugs that specifically inhibit cancer growth factors. These are more effective, with fewer side effects compared to traditional chemotherapies. They are already available for specific cancers in dogs such as mast cell tumours and melanomas.

Ionising radiation also kills cells, and irradiation is now used as a carefully focussed, computer-mapped beam to treat certain specific cancers in pets, as in people. This does require expensive facilities, and it is not yet available for pets in Ireland.

Immune based therapies are the most recent and promising type of treatment for cancers are: this includes infusions with special immune cells, therapeutic cancer vaccines against specific cancer antigens and gene therapy, where the damaged genes in cancer cells are replaced by healthy genes

Treatment of cancer is rapidly developing, led by research at universities and other institutions.

For pet owners, the main message is that much more can be done now than in the past. Cancer may be a serious challenge, but science is tackling that challenge in new and exciting ways.

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