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AskHQ: Melanomas

Q: Is it possible for horses who are not grey to get melanomas?

A: Melanomas are much rarer in horses with non-grey coats, but they can and do occur. Unfortunately, when these tumours appear in non-grey horses they tend to have a much worse prognosis, as they are more aggressive. When melanomas occur in grey horses, it is common for them to be benign, and therefore they may grow locally but are unlikely to spread throughout the body, causing damage to other structures or organs. However, when melanomas occur in horses with other coat colours, they are typically malignant and aggressive and therefore spread throughout the body, affecting other organs. This can happen early in the disease, and in these cases there is a very poor outlook for the affected horse.

Melanomas in non-grey horses tend to have a different appearance to those seen in grey horses. They commonly occupy the same locations as melanomas in grey horses, but they can also be found elsewhere on the body – even in the hoof wall or coronary band of the foot. Melanomas in the non-grey horse may or may not be pigmented, which often causes some delay in diagnosis. In essence, the tumours, while being the same kind of tumour as those occurring in grey horses, have different appearances and behaviours in horses with different coat colours.

As these tumours are so aggressive in non-grey horses, any suspected melanoma in these animals should be evaluated by a vet immediately. Typically, a vet will need to take a biopsy of the mass to assess its composition. This will tell the vet what exactly the tumour is, and then decisions can be made about the way forward. In the case of melanomas in non-grey horses, rapid action will need to be taken, but even when the vet is prompt to remove the tumour and apply treatment, melanomas in non-grey horses commonly prove fatal for the animal.