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Managing canine osteosarcoma: limb sparing versus amputation?

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Dr. Igor Vasilev

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The question of whether to euthanase a dog or to amputate or spare its limb in the management of canine osteosarcoma was a subject debated at this year's BSAVA congress, held in Birmingham from March 31 to April 3. Arianwen Morris reports

 

OSTEOSARCOMA is a very aggressive cancer arising from the bone-forming cells within the cortex or the inside of the bone. It progresses rapidly to involve the adjacent soft tissue, causing intense pain. As the tumour growth process weakens the bone, it can ultimately result in fracture. This was explained by Jane Dobson, an RCVS specialist in veterinary oncology at Cambridge university, during a session called 'Canine bone tumours: limb sparing versus amputation', which was part of the congress's 'controversies' stream.

 

Bone cancer was 10 times more common in dogs than in people and 85 to 95 per cent of bone tumours affecting the metatheses of the long bones in dogs were osteosarcomas, she said. There were a number of debatable issues concerning canine osteosarcoma, including the method of its diagnosis, for example, radiography versus biopsy, the system by which its progression should be graded and, in particular, the ways in which it should be managed.

 

The major issue to address when considering the management of a patient was pain: 'For the animal's welfare, we have to address the pain aspect,' she said. However, another feature of the disease was that metastasis occurred very early on in its progression and was a complication in approximately 90 per cent of cases.

 

'This occurs very early in the course of disease and, unfortunately, there's no such thing really as getting in there early, amputating the limb and saving the animal from metastasis – that doesn't happen. They have microscopic deposits at the time that they become lame,' said Dr Dobson.

 

Amputation was the 'gold standard' treatment. 'It's the fastest, sure-fire way of relieving the pain that animal is suffering,' she said. 'Amputation also achieves what we call a compartmental resection, which is what is required to remove, in its entirety, a sarcoma.

 

'The downside is that this doesn't cure the animal. If no further treatment is administered, the mean survival time is only three or four months.'

 

Even with chemotherapy to delay the spread of metastatic disease, life expectancy was only about one year, so the ethical dilemma was whether it was in the animal's best interests to interfere – by amputation or by providing limb-sparing surgery – if it was unlikely to live very long.

 

'The option that needs to be chosen by consultation between yourself and the client is the one that suits them, suits their dog and the one that you've got the skills to do or will refer to be done,' she said. On a slide listing possible treatments, it was not by mistake that euthanasia came first. The question was not 'Is euthanasia an option', but 'When are you going to euthanase that dog?'. 'At the end of the day, we have to remember that this is a fatal disease and it is not yet in our power to stop it metastasising in the vast majority of cases.'

 

Clinical indicators were useful to tell whether a dog was likely to be a long- or short-term survivor, and therefore whether intervention was appropriate. For example, dogs with lower or normal alkaline phosphatase levels at the time of diagnosis survived significantly longer than dogs in which it was elevated. Young age was a poor prognostic indicator, as was large tumour size or it being positioned in the humerus.

 

Informing human science

One argument for performing surgery, including limb salvage, in dogs was that experiences with treating dogs could be used to inform better management, diagnosis and treatment of human bone cancer.

 

'Treating tumours in dogs is great for the canine population, but actually, because these tumours are so much more common in dogs and because dogs are a similar body size to some extent as people, treating dogs with bone cancer can actually have some very useful spin-offs and inform how to manage people with bone cancer,' said Dr Dobson.

 

Breed dispositions to osteosarcoma suggested that it was associated with large or giant breed dogs and more prevalent in those with a rapid growth rate. In people, bone tumours were more common in adolescents. This had led to studies on the role of various growth-related proteins. 'A lot of work has been done on gene expression profiling of canine osteosarcoma, which has resulted in some differences in gene expression being identified between dogs with long and short survival times. Overexpressed genes in short-term survivors are associated with roles in proliferation, drug resistance and metastasis,' she said.

 

 

 

For example, ezrin, a membrane cytoskeleton protein, had been shown in a large number of dogs to be associated with a shorter disease-free interval. This marker had become very significant in human patients as well.

 

Recently, an agent called muramyl tripeptide had been licensed in Europe for the treatment of human bone cancer and was currently under consideration by NICE in the UK. A lot of the data used to support its licensing had come from clinical trials on dogs, she explained.

 

'The dog is a very suitable preclinical model for therapeutic approach. This isn't using dogs as experiments. It's actually using the clinical treatment and management of dogs to inform what goes on in people.'

 

Showcasing cutting-edge limb-sparing technology that could be used in the treatment of cases of neoplasia or trauma was neuro-orthopaedic veterinary surgeon Noel Fitzpatrick of Fitzpatrick Referrals, who gave a talk called 'A licence to kill, save or chop'.

 

Professor Fitzpatrick was also in support of the 'One health, one medicine' concept. As this year marked the 250th anniversary of the modern veterinary profession, he said it was time that the veterinary and human medicine professions worked together again: 'The future is a symbiosis of human medicine and veterinary medicine reconverging.'

 

In his team, doctors and vets worked together to treat both animals and people. He fully supported Dr Dobson's view: 'Humans can't move on without us, but we shouldn't be doing this as an experiment. We should be doing it because it's in the interest of both species,' he said.

 

At his referral practice, Professor Fitzpatrick performed surgery to provide limb amputation prostheses with a hydroxyapatite collar – a technology pioneered by Gordon Blunn of University College, London, which allowed bone to grow into metal.

 

Among the dogs he had treated were Charlie, a labrador that had undergone limb-saving surgery for bone cancer, and Mitzi, which had been fitted with an intraosseous transcutaneous amputation prosthesis (ITAP) (see box). With reference to the ITAP, he said, 'You might think this is just a piece of plastic.' However, about US $85,000 worth of engineering effort had gone into designing it like a ski boot so that it would break before the dog's leg did.

 

 

There was no doubt that these procedures could be done, but should they, he asked. 'Do we take the middle road between nothing can be done and everything should be done?'

 

Professor Fitzpatrick believed that the patient's interest was the only interest and that, providing there was reason to believe that the procedure offered would give a reasonable quality of life, it would be wrong to withhold it as an option from the owner.

 

'It's our moral responsibility, in my opinion, to offer owners all of the choices, because, while many animals will do great on three legs – and I want to go on record for saying that – some will not,' he said.

 

There were, however, a number of common objections to limb sparing in animals. These included comments such as 'We're fine as we are. Why change?' and 'It's putting the animal through too much.' People often questioned the expense involved, but, he said, it was not the vet's remit or job to decide what an owner could or could not afford. 'Don't ever assume that people do not have the wherewithal,' he said. 'It's their decision.'

 

It was also no longer the case that there was not enough evidence to support the procedures.

 

He could not understand anyone who said 'It's only a dog' or 'Dogs and cats simply don't deserve the level of care afforded to humans'. 'Who says that?' he asked. 'That's why we signed up for our professional lives to treat them.'

 

Vets had responsibility not only for the relief of animal suffering, but also for advancing medical knowledge, he added. 'It is important that the veterinary profession accepts that. It is not, in my opinion, for us to take away the freedom of choice, but to guide and support and do our best for each and every patient.'

 

Limb sparing: a step in the right direction?

Professor Fitzpatrick gave three examples of dogs that had undergone successful limb-sparing or amputation procedures – Charlie, Mitzi and Obi (clockwise from right).

 

Charlie had been treated for bone cancer and was extremely lame when presented for treatment. After removal of the tumour, an endoprosthesis was fitted inside the affected leg and the dog was still doing well 17 months later.

 

'Does he have good function?' asked Professor Fitzpatrick. 'Yes he does.'

 

'Did he go through too much suffering? No. Is it right for all patients? No. Would he manage on three legs? Probably, but do we have the right as a profession to withhold a leg from him now that we can do it?'

 

Mitzi, a three-and-a-half-year-old white German shepherd dog whose foot had been crushed by a horse, had received an intraosseous transcutaneous amputation prosthesis (ITAP), which involved the implantation of a titanium rod into the bone, onto which skin could attach and a prosthesis could be fitted. The technology had been developed for dogs by Gordon Blunn of University College, London, in association with Professor Fitzpatrick and was now being used to help victims of the July 2005 London bombings.

 

The technology that allowed this had been developed on the human finger, and had then been upsized to the dog, said Professor Fitzpatrick. While Mitzi had not had cancer, it was an example of what was possible.

 

Obi, a 12-year-old Jack Russell, had lost a leg in a traffic accident two years ago and was an example of a dog continuing to lead a healthy life on three legs following amputation.

 

 

 

 

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