Melanoma treatment trialled for grey horses

Specialists at Liverpool and Glasgow universities are pioneering research they hope will lead to a greater understanding of melanoma.

The cancer, which can be fatal, afflicts 90% of grey horses.

Professor Derek Knottenbelt said he has been using a chemotherapy agent that is injected into specific advanced tumours that are inoperable.

The research is “in the extremely early stages but it does hold some promise”, he told H&H.

Melanoma, a skin cancer, is common in greys, but is rarely treated because of concerns the tumour will spread. There is no available effective chemotherapy for horses.

Vets usually advise the tumours are left alone, Dr Knottenbelt said, believing that interference could cause more trouble. Many affected horses die from other causes before the melanomas become a serious issue.

Professor Knottenbelt said most melanomas will eventually become malignant, so an apparently small, benign mass can become dangerous and even fatal.

Little research has been done into the disease, which affects almost all grey horses.

Melanoma does not just affect the skin. Professor Knottenbelt has seen tumours “in almost every organ of the body, including inside the eyes”.

Sam Chimley, of Leicestershire, said her 19-year-old grey mare has a large tumour near her anus, but her vet told her to accept it as part of owning a grey horse.

Rather than “take no for an answer”, Mrs Chimley has started treatment of four to six injections under sedation at fortnightly intervals, which could shrink the tumour.

Dr Knottenbelt said the lack of research was a “disgrace”.

“Around 75% of grey horses will develop malignant melanomas,” he said.

“Then when they are bad, treatment is not possible so it becomes a self-fulfilling prophecy. They are benign initially but in the later stages of their development, they are almost always malignant.

“Malignant tumours have the potential to be fatal. If that transition takes place when the horse is nine, or 10, or 12 years old, and the melanoma spreads throughout the body, it will in all likelihood be fatal.”

This news story was first published in Horse & Hound magazine (4 April 2013)

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