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TREATMENT OF CANCER
Different treatments have different abilities to get rid of cancer cells. There are some cancers which are only treated by chemotherapy (e.g. lymphomas) for instance. Otherwise surgery is the first line of attack, radio- and chemo-therapy are next in being able to destroy large tumours (large in this instance means a few cms across) and immunotherapy is only likely to be of any benefit when there are just a few cancer cells left in the body.
The most effective treatment by far for almost all tumours is surgery. If done early and effectively it can cure completely a large proportion of tumours which would otherwise become life-threatening. Except in very advanced cases with large numbers of secondary tumours, surgery can remove 95-100% of tumour cells.
It is important to assess the patient in detail before embarking on surgery. This assessment may involve just a physical examination in the case of a small, early and relatively non-threatening tumour, but more dangerous tumours or more advanced cases should be staged properly.
Surgery to remove a tumour will involve the removal of normal tissue around the tumour, so that the operation scar may be larger than the owners expect. Too little margin of normal tissue is a common reason for recurrence, but even the most experienced oncological surgeon will be caught out occasionally. Samples sent to the laboratory after surgery should be checked for adequacy of removal.
If a tumour is large, it may be necessary to use complicated reconstructive techniques to repair the region. In some parts of the body it is impossible to remove the tumour witjout removing a body part. A leg will usually need to be amputated if the patient has a bone tumour, for instance. This would only be done if the remaining limbs were capable of supporting the animal and allowing it to exercise.Go to top of page
There are three uses for chemotherapy: therapeutic, adjuvant and palliative.
Therapeutic chemotherapy is used particularly in lymphomas and related tumours. Here, no attempt is made to remove the tumour, usually because it is in many parts of the body. Instead, drugs are given which kill tumour cells.. This can occasionally cure the cancer, but more often, whilst the lumps disappear, they will recur one day. This is because within a tumour there will be some cells which are resistant to treatment. These will eventually grow and form further tumours which will not respond to the drugs used before. The aim of treatment is to get rid of symptoms of illness and to prolong active, happy life.
Adjuvant chemotherapy is used after an operation when it is suspected (or known) that there are still tumour cells left in the body, either in the local area or in other organs. If chemotherapy is given straight after surgery, there will only be a small number of cells to kill, and these will tend to be more sensitive than cells in a large tumour. So a course of anti-cancer drugs given during the few months after surgery can dramatically improve the chances of cure, or at least increase disease-free survival.
Palliative chemotherapy can be used in advanced cases where the tumour is causing pain. Many patients will become more confortable, at least temporarily, if given anti-cancer drugs.Go to top of page
In the treatment of cancer in humans, radiotherapy is very widely used. It is very much less used in pets because of costs and health and safety at work issues.
There are two main methods of using radiation to destroy cancer cells. Either a radioactive material is put into a tumour or radiation is fired at the tumour from outside the body. The first method (brachytherapy) is used in one or two centres in the UK to treat thyroid tumours in cats, but involves the cats being confined in isolation for about 2 weeks: other methods of treating these benign tumours are available. Any patient receiving brachytherapy will be a radiation risk to people and other animals in close contact with it. It is, therefore, a troublesome method.
Teletherapy, when the radiation is produced by a machine and beamed into the body does not make the patient radioactive and so the only risks to others are associated with the radiation machine itself and this can be shielded with thick walls and doors. The cost of the machine and building is very high, and there are 3 centres currently (2008) offering teletherapy for pets in the UK. These are at University of Cambridge, VRCC in Essex and University of Liverpool.
Treatment patterns with radiation are complicated and lots of small doses quite close together are better, both for effect and safety, than fewer, larger doses. Unlike humans, pets have to be anaesthetised to keep them perfectly still in the radiation beam. The balance between number of anaesthetics and effects (useful and undesirable) of the treatment is not easy to strike.
Radiotherapy has side-effects on tissues in the area irradiated and, to some extent, on the rest of the patient. Again, pets are more difficult than humans in that sore skin will be licked, scratched or rubbed by pets whereas humans can be told to leave it alone.Go to top of page
The body's immune system can destroy tumour cells if it can detect them as abnormal. There has been much experimental work done in the last 100 years looking at ways to stimulate the immune system to assist in treating cancer.
It is known that occasionally tumours can disappear. This is probably caused by an attack by the immune system. Bacterial infection of tumours has been associated with this and attempts have been made to inject bacteria into tumours with varying success. BCG vaccine (the human TB vaccine) has been used in various ways, especially in the management of melanomas. Trials have been found not to be reliably repeatable, though some notable success have been reported.
Another method of stimulating the immune system is to make vaccine from tumours and use them to try to get the body to attack any remaining cancer cells. In combination with bacterial vaccines, there have been some interesting results, but still nothing really repeatable.
There are arguments in favour of including immune stimulation in some form in the management of cancers.Go to top of page
Most established treatments for cancers aim at killing the cancer cells. This is not always possible but many patients have no serious symptoms caused by their tumours and if the tumour can be stopped from growing, this can allow for an extension of good quality life. Metronomic therapy aims to do this and its use is increasing in both humans and pets.
For a tumour to grow it must cause the body to form new blood vessels to supply the tumour with nutrients (angiogenesis). There is nothing clever on the part of the tumour in this: normal body tissues will produce chemicals which stimulate new blood vessel growth to help repairing injuries so that all the tumours do is produce more of these chemicals. If the tumour cells did not produce the angiogenetic chemicals, they would not grow into a tumour. There is a lot of research going into finding ways to stop this angiogenesis and several drugs have been found to do this. The good thing is that most of these drugs have few or no side-effects.
A few chemotherapy drugs have been shown to block angiogenesis when they are given in smaller than usual doses over a long period. Adding certain anti-inflammatory drugs increases this benefit and some antibiotics have been shown to add further to this effect. There is a lot we still need to find out about this process and it may not simply work via anti-angiogenesis, but we can apply this type of treatment to a lot of patients which we would have been unable to offer any hope to in the past.Go to top of page
Miscellaneous and experimental therapies.
There is much research under way in the general field of cancer treatment. Particularly, the idea of producing anti-cancer drugs which specifically attach to cancer cells is a continuing challenge. If cytotoxic drugs could be attached to antibodies which would recognise tumour cells and concentrate the drug within cancers, the side-effects would be minimised and more aggressive doses of drugs would be delivered to the tumour.
The work being done on identifying the differences between cancer cells and their normal counterparts is essential to this, and other lines of attack on cancers. It is to be hoped that new treatments will become available within the next 5-10 years.Go to top of page