Seminar 2005

 

This was held at Stoke Goldington Village Hall on Sunday, July 31st.

The morning speaker was Malcolm Brearley on cancer and, more specifically, osteosarcoma. Malcolm Brearley, MA VetMB MSc(Clin Onc) FRCVS is one of only three RCVS-recognised specialists in Oncology and is Europe's leading Veterinary Oncologist.

In the afternoon the speaker was Miranda Brace on the history, form and function of the breed, aided by a hound - Bokra Sequel - kindly loaned by Sandy Surrell and Kathy Coleman of the Bokra kennel, and ably handled by Jeff Crawford.

Your pet and cancer

 

What is cancer?

Cancer is the common name given to all the various forms of malignant tumours. A tumour is a mass of cells that are growing out of control. There are two main types of tumours.

 

Malignant tumours or cancer are the most aggressive; they invade into the surrounding tissues and have the ability to spread to other parts of the body. It is this ability to produce secondary tumours that makes them so life threatening.

Benign tumours only grow locally and never spread. They can however cause serious problems just because of their physical size or position.

How can tumours affect the patient?

This depends upon where the tumour is and what type it is. When small, most tumours do not cause a problem; only when they are large do they affect the patient but by this stage they may be untreatable. As a general rule, malignant tumours (cancers) are more life threatening than benign tumours because of the risk of spread throughout the body.

 

There are many different types of cancer and each behaves in a slightly different way. It is therefore important to have a sample of the tumours sent for examination by a pathology laboratory.

 

Ten common signs of cancer in animals

1. Abnormal swelling or lump that grows

2. Sores that do not heal

3. Loss of appetite

4. Offensive breath

5. Unexplained loss of weight

6. Difficulty eating or swallowing

7. Persistent lameness or swiftness

8. Difficulty urinating or defecating

9. Breathlessness or loss of stamina

10. Bleeding or discharge from any body opening

 

What should I do if I find a lump on my pet?

Not all lumps turn out to be tumours but it is important to ask your veterinarian to have a look when you first notice one. A small tumour, even a cancer, is more likely to be cured if it is treated early. A biopsy may be necessary to determine the exact nature of the lump. "Let's wait and see" is not a good option.

 

Cancer can be treated - and often cured

As in people, many tumours are readily treated and many can be cured. Early diagnosis and appropriate treatment are the keys towards a successful outcome. Your pet cannot choose what cancer they will get but you can choose the best course of action.

 

The cause of cancer in dogs and cats

 

The scientific basis of cancer

Every cell of the body is normally under very strict control imposed by the body as a whole. Very occasionally, a cell acquires the ability to divide and grow outside this normal control and a cancer develops. This happens when a number of genes within a cell change or mutate. Mutations occur in all of us all the time - in deed without mutations, evolution could not have occurred and life would have remained as the sludge at the bottom of a primordial sea! Most of the time, these mutations come to nothing but occasionally they cause the cell to go wrong and develop into cancer.

 

Known causes of cancer ("risk factors")

For an increasing number of human cancers the cause is known. Some of these risk factors are smoking (for lung cancer), certain viruses (cervical cancer) and ultra-violet sunlight (skin melanoma). In addition, certain genes that are present in families have been identified (e.g. BCR and breast cancer in women).

In dogs and cats, there are only a few known risk factors for cancer. In cats, the virus known as Feline Leukaemia Virus (FeLV) is a definite trigger for certain cancers (feline lymphoma and leukaemia). However, not all cats that are infected by FeLV will develop cancer and, conversely, not all lymphomas in cats are induced by FeLV infection.

Another example of a cancer for which there is a known cause occurs in white-faced cats that sit out in the full sun. The relatively hairless pink areas of the ear tips, eyelids and nose are prone to sunburn which in turn can progress to skin cancer.

 

Breed related cancers

Certain breeds of dog appear to be susceptible to specific tumours. This may be related to the characteristics of the breed or due to a genetic predisposition. Bone cancer is more common in giant and large breeds such as Great Danes, Irish Wolfhounds, Rottweilers, and St Bernard's. This is thought to be related to the rapid growth characteristics of the adolescent pup although there is also evidence for a genetic susceptibility in some of the giant breeds.

For example, Boxers have a relatively high incidence of tumours of the skin and the brain. Bernese mountain dogs appear to suffer from a variety of malignant cancers with a tendency to affect a younger age group than dogs as a whole. Similarly Flat-coated Retrievers tend to have a relatively high incidence of cancer which behaves more aggressively than in other breeds of dog. These and other breed related tumours are highly suggestive of a widespread genetic susceptibility for the specific cancer associated with the breed. However, truly hereditary cancers (i.e. that are passed down in certain lines) are rare in dogs.

Further research will identify specific causes of cancers in dogs and cats and may lead to novel ways of treating them. More importantly as the specific causes become know then specific ways of preventing that cancer may be possible.

Bone cancer in dogs

Bone tumours affect the larger breeds and are rare in small dogs. Irish wolfhounds, great Danes, Rottweilers and German shepherd dogs seem to be at particular risk. To date, no genetic factors have been identified and it is thought that the growth characteristics of the at-risk breeds are important. Tumours tend to arise in the limb bones with the most active growth. The commonest sites are the distal radius (near the wrist), proximal humerus (near the shoulder), distal femur (above the knee in the back leg), proximal tibia (below the knee) and distal tibia (above the hock).

 

Presentation

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Middle-aged dogs are more commonly affected. The first clinical sign that is noticed is either sudden onset lameness or a swelling at one of the characteristic sites. Not all sudden lameness and swellings are bone tumours - joint injuries such as sprains or ruptured ligaments can also cause these clinical signs. Veterinary attention should be sought at an early stage in all cases. With bone cancer, this lameness progresses and the dog may become 'grumpy' and off colour. Bone tumours become intensely painful, so much so that the dog can be severely affected by this. As the tumour grows, the swelling and lameness increase and routine painkillers give little or no relief.

The commonest bone tumour is the type known as osteosarcoma - a malignant tumour arising from the bone cells. Less common tumours
include fibrosarcoma (from fibrous tissue), chondrosarcoma (cartilage origin), and haemangiosarcoma (blood vessel origin). X-rays can be used to detect a bone tumour but laboratory examination of a biopsy is necessary to determine the exact nature of the tumour.

 

Prognosis

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The prognosis for any bone tumour is grave. Without treatment, the primary tumour becomes so painful that euthanasia is the only humane option. Almost all bone tumours of the legs are malignant (cancerous) and therefore have the potential to spread. In the case of osteosarcoma, secondary spread to the lungs is an almost certainty but are rarely detected on x-rays at this stage. However, even when the primary tumour is removed, these secondary tumours continue to grow to such a size that severe breathlessness and general malaise become over-whelming.

 

Treatment options

There is no simple treatment for bone tumours in dogs. Bone cancer is aggressive and therefore requires aggressive therapy to achieve any chance of success. However, in recent years, progress has been made:

 

Pain relief is the first and foremost consideration. This can be achieved with analgesic drugs or by radiotherapy to the primary site. The pain relief achieved by radiotherapy tends to be better and of longer duration than by drugs but even so the pain is likely to start up again within the next 6 - 9 months. However, not all bone tumours are suitable for radiotherapy. Radiotherapy has no effect against the secondaries.
 

Amputation is the only certain way of controlling the pain and the primary tumour itself. The pain associated with the tumour is often so severe that the dog is walking on three legs; if they can manage at this stage, they will be so much happier and pain-free following amputation. Most dogs will cope very well with amputation; even Rottweilers and Great Danes will adjust to the loss of a forelimb. As an alternative to amputation, so-called limb-salvage operations have been tried where all of the affected bone is removed and replaced with a bone graft, a large metal plate and fusion of joint. This option is fraught with major complications and is rarely performed in Britain.
 

Anti-cancer drugs following amputation are used to control the rate at which secondaries develop. With amputation alone, 60% of dogs will die from secondaries by six months; only 1 in 10 dogs will survive to one year. With the addition of anti-cancer drugs the six months survival is about 60%, with 4 in 10 alive at 12 months and about 15% alive at two years. Although generally well tolerated, the drug treatment can cause occasional side effects; some nausea and vomiting may occur after the treatment but this usually resolves within a couple of days. Currently the drug is administered once every 3 weeks for four doses.

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