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Oncology:

(Referral oncology cases now welcome...see PetCancerVet website)

Tumours are very common in pets and most people find them frightening. As long as they are dealt with promptly, most of them need not be feared.

About half of tumours are benign and the only problems they pose relate to their size and position. They will generally require surgical removal. The most important thing is to tell which tumours are benign and which are malignant.

There is no way to tell if a tumour is benign or malignant without examining at least a few cells from it. Benign fatty tumours are very common, some dogs having several. However there are two malignant tumours which can look and feel exactly like them. The simplest way to check tumours is by Fine Needle Aspirate Biopsy in which a needle attached to a syringe is inserted into the tumour and cells sucked from it. These can be stained and examined under a microscope. I do this regularly and I can diagnose several tumours reliably, and get a fair idea about many others. It is sometimes necessary to send the cells away for expert examination to be sure. Sometimes the FNAB will give a good enough idea for reliable surgery and the complete tumour can be sent away for full examination.

I am building an Internet resource of photomicrographs of tumour cytology on my PetCancerVet website.

Cancer cells from FNAB of colon tumour from Mogsy C

Now with a special stain which marks areas in the cell nucleus associated with recent cell division (AgNORs) it is possible to get a better idea about the degree of malignancy of tumours which are otherwise difficult to assess. The stain can be used on FNAB smears and I shall thus be able to get a better idea of the aggressiveness of a tumour before surgery. Here is an example of a malignant behaving tumour which on normal examination of the cells appeared relatively non-aggressive.

The darker brown marks are the AgNORs (x1000 mag)

Surgery is the first line of treatment for most tumours and as long as it is carried out in time, and with sufficient margins to ensure that no tumour cells are left, it can be a permanent cure for many malignant tumours. Before embarking on surgery it is desirable to look for evidence of tumour spread by x-ray or scan. The main factor limiting this is that tumours do not spread as lumps, but as minute clumps of cells very much too small to detect. So a negative x-ray or scan does not guarantee that the tumour hasn't spread. I prefer, however, not to do major operations on animals whose tumours are already advanced in other parts of the body.

After surgery, if there is a significant risk of the tumour having spread, it may be useful to use drugs to try to kill any remaining tumour cells. It is best to try this when as much tumour as possible has been removed and as early as possible in the growth of any secondary tumours. This 'adjuvant chemotherapy' is given to an animal when it has no actual signs of tumour. Its aim is to kill any small clumps of cells that may have spread.

Ultrasound scan of malignant bladder tumour in a dog. This was removed surgically and followed by six months chemotherapy during which the dog was WELL and she is still alive and well 5 years later

The other use of drugs is in tumours which develop in many places at once such as lymphomas (tumours of the lymph glands) which are quite common in dogs.

These are AgNOR stained samples from two lymphomas. The one on the left is a very low grade one with only 1-2 AgNORs per cell: the righthand one is a malignant one with an average of 6 AgNORs per cell.

In humans, chemotherapy is used aggressively and most people receiving it are ill because of the drugs. In pets, it is difficult to justify causing severe side-effects, so less aggressive treatment regimes are generally used. My aim is always to allow the pet to feel as normal as possible during treatment. Whilst the drugs used in treating tumours are dangerous and can cause severe side-effects, these are dose related and can almost always be minimised. If a particular pet has worse side-effects than usual, I would modify or even abandon treatment.

Some situations call for a palliative approach rather than attempts at definitive treatment. In general it is possible to alleviate some or all signs of the tumour's effects on the pet without surgery or aggressive chemotherapy. The tumour is, however, still present and will progress to cause unacceptable problems to the pet in time. The position of the tumour, the extent of spread, the cosmetic effects of possible surgery, cost considerations may all weigh in deciding on the approach to a tumour.

An interesting development in palliative care is the use of non-steroidal anti-inflammatory drugs to suppress tumours. Bladder and large bowel cancers have been shown to be reduced in size and slowed in development by certain NSAID's and I am particularly interested in the drug Meloxicam which is licensed for use as a pain-killer and anti-inflammatory in dogs and cats. The British Veterinary Oncology Study Group is planning a study into the effectiveness of this drug, but results will take some years to evaluate. If you are interested we have a website at this link.

There is a web site bringing together owners of pets with chronic illnesses. Click this link.>

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