Cancer- a General Discussion
Hearing that your pet has been diagnosed with cancer can be very distressing. In this article I will try to give a general overview of cancer in animals. This is a huge topic and there are many different types of cancer which can affect our pets. If you know the specific type of cancer affecting your pet you should seek further information about that particular disease after you have read this article.
Neoplasia in another word for cancer. Neoplasia literally means "new growth". Neoplasia occurs when a cell develops a change in its DNA and then is able to reproduce itself in an uncontrolled way to produce cancerous tissue. The clinical disease which results from this process will depend upon what type of tissue and/ or organ is affected.
It is unclear exactly what causes the DNA in a particular cell to change (or mutate), although there are many known factors which may make cancer more likely to occur. Exposure to carcinogens such as certain chemical substances (both natural and man-made) and exposure to radiation may predispose an animal towards the development of cancer. Genetic factors are also possibly involved.
Once a cell has mutated it must be able to replicate itself in a totally uncontrolled way to form a tumour. It is thought that many cells in the body develop faulty DNA (mutate) but not all of them are able to escape the body's control mechanisms and replicate themselves. Most mutated cells are recognized as faulty and destroyed by the immune system or die off spontaneously, but those which go on to form cancerous growths escape this protective mechanism and proliferate. Why some mutated cells are able to escape detection or destruction by the immune system is unknown. Proliferation of cancerous cells will obviously give rise to cancerous tissue in the affected organ.
The way that a tumour or cancer will affect an individual animal will depend upon many factors. Some cancers are quick to grow and spread throughout the body. It is usually these malignant types of growth which most people think about when they hear the word 'cancer'. If a tumour is malignant it will spread away from its original location to other organs within the body. It may invade other local structures and spread aggressively throughout neighbouring organs. Alternatively it may reach distant organs via the blood or lymphatic system. This spread or invasion of cancerous cells is known as metastasis. When metastasis of cancerous cells has occurred the treatment of cancer is less likely to result in a favorable outcome. Other types of cancer are slow to grow and do not spread away from their original location. Generally these benign tumours are less serious and easier to treat than the malignant types of growth. Of course there are many variations in between these two extremes. The location of a tumour is also important to consider when thinking about the likely outcome for an animal. For example even a very slow growing benign tumour is likely to cause serious problems if it is within the brain. Another problem which it is necessary to consider is whether the tumour secretes hormones or has other effects which disrupts the normal physiology of the animal. All in all there are many possible consequences of neoplasia in animals and the exact course of the disease for any pet will depend upon the type of cancer and other individual factors.
When attempting to diagnose cancer in animals many techniques may be used. In many cases a vet will be able to see or palpate tumours or other clinical signs may indicate that a tumour may be present. Often X-ray or ultrasound images are used to get a clearer idea of the problem: these techniques can often give a clear indication of the presence of a growth. Other imaging techniques such as MRI or CAT scans may sometimes be used if your pet has been referred to a specialist veterinary hospital. These types of techniques will give an indication of the presence of a mass or "lump" but will not give specific information about the type of cells involved. This information is usually needed so that a definitive diagnosis can be made. This often requires a biopsy sample to be taken. The exact procedure for taking the biopsy sample will depend upon the position of the tumour among other factors.
Once a definitive diagnosis has been made it is necessary to consider the treatment options for the pet. Treatment of cancer in animals will depend upon the type and position of the tumour, the general health and condition of the animal and owner preferences. In some cases it may be kindest to provide palliative care only rather than subject the animal to treatment which is not likely to be successful. Often however there is a chance that more aggressive treatment will help the animal, either by achieving a complete clinical cure or by providing a better or longer life for the pet. Surgery is often performed either to try to completely remove the tumour or to de-bulk it and prolong the life of the animal. Cryotherapy may also be used in some tumours to freeze and destroy them. Chemotherapy and radiation are also used to treat tumours in animals but often these types of treatment will only be undertaken at specialised establishments where the equipment and expertise are available. If an animal's quality of life is severely compromised due to cancer, euthanasia may sometimes be the most humane option rather than attempting any treatment.
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