They can metastasise to other organs in the body, but it can take years before they start to become problematic.
While those under the tail are slow-growing, they can develop to a size where it becomes difficult for horses to pass faeces normally.
• There is no evidence to suggest that metastasis is more likely to occur if small melanomas are removed surgically and so it may be sensible for your vet to remove these at an early stage while they are still small.
For the full article on equine cancer, see the current issue of Horse & Hound (16 April, ’09)
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