Cancers are diseases that occur in most animals, including dogs. A cancer results when a cell in a dog’s body starts to replicate uncontrollably, forming clumps of abnormal or cancerous cells called tumours. These cancer cells escape detection and trick the natural killer cells of the body’s immune system into not attacking and destroying them. Having eluded the body’s defences, cancer cells embark upon an eternal life of producing countless generations of descendant cancer cells.
Genes and cancer
Some individuals carry genes that predispose them to certain cancers. The Bernese Mountain Dog, for example, has a 60 per cent chance of dying as a result of cancerous tumours.(edit:- Since publishing this article, I have been contacted by several Bernese Mountain Dog breeders who claim to have bred animals with far lower incidences of cancer. I have no reason to doubt this, but please do ensure you check out the breed history of any pure bred dog you purchase) In other breeds, the genetic link can be much more complicated. Individuals may inherit a cancer-producing gene but also a cancer-suppressing gene, and even another gene that suppresses the cancer-suppressing gene. In addition, these genes can be turned on and off by a host of environmental factors including ultraviolet light, radiation, and various chemicals.
Names are important
Cancers are classified according to the part of the body in which they originate. Carcinomas, for example, arise from the tissues that line the internal and external surfaces of a dog’s skin and organs, while sarcomas arise from within tissues such as muscles, blood vessels, and bones.
While sophisticated diagnostics, including body scans, can help to identify potential tumours, a sample of tissue from the suspected area is necessary for an accurate diagnosis of cancer. Small tumours may simply be removed, but for larger ones, your vet may either take a small piece of suspect tissue (a biopsy), or use a needle and syringe to withdraw a sample of cells to be analysed. Cancers generally occur later in life, but can also affect younger individuals. Early diagnosis is vital, and dogs over seven years old should have yearly preventative veterinary examinations.
Common signs of cancer include:
- Abnormal swellings that persist or continue to grow;
- Sores that do not heal;
- Weight loss;
- Loss of appetite;
- Bleeding or unusual discharge from any body opening;
- Offensive odour;
- Difficulty eating or swallowing;
- Hesitation to exercise or lack of stamina when exercising;
- Persistent lameness or stiffness;
- Difficulty in breathing, urinating, or defecating.
Surgery is usually the most effective treatment for cancer, but if it is impossible to completely remove the tumour or if the cancer has spread to other parts of the body, radiation therapy and chemotherapy may be used. New treatments for cancer have also been developed that may prove very effective; these include drugs that selectively cut off the blood supply to the cancer, or that stimulate a dog’s immune system to attack the tumour. Gene therapy allows cancerous cells to be specifically targeted and destroyed.
In some cases, however, you and your vet may make the difficult decision that, rather than embarking on a potentially distressing course of treatment, it may be preferable to go for a good quality of life for your dog, even if this will inevitably mean a shorter life expectancy.