Home Health and vet Melanomas: Not always as innocent as you think!

Melanomas: Not always as innocent as you think!

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By  Equitom: Dimitri Kadic, DVM, Diplomate ECVS-ACVS and
Liesbeth Haegeman, DVM, resident ECVS
Photography: Courtesy Equitom
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Melanomas are among the most common tumors in the horse. They are almost exclusively seen in grey horses, where they are generally benign. Despite being described as ‘benign’, they are often accompanied by great discomfort to the horse and can even become life-threatening.
The idea that is spread in the equine world that melanomas are ‘normal’ in grey horses and that there is no need to be worried about them, is incorrect. With tumors, melanomas, and others, it is always advisable to consult a veterinarian so that if necessary the right treatment can be initiated in time. The most typical places where melanomas form are in the skin around the anus and the base of the tail (image 1), but these tumors can also occur in other places. In some cases, they become malignant and can metastasize within the rest of the body.

Etiology

Melanomas are tumors of the melanocytes (pigment-producing cells). Normal melanocytes produce pigment that is passed on to skin and hair cells thus giving color to skin and coat. If these melanocytes degenerate, bumps with black tissue on the inside (melanomas) are formed (image 2). Up to one third of all tumors in the horse are melanomas. They are seen almost exclusively in grey horses, but can in rare cases occur in colored horses too.

Grey horses

Approximately 80% of grey horses over the age of 15 have melanomas. The cause of the high incidence in grey horses is believed to be linked to the same genetic basis as being ‘grey’; this is basically also a disorder of the melanocytes. For example, it was seen in Lipizzaners that horses homologous to a particular gene (i.e., who have inherited the gene from both father and mother) become white faster and more uniformly and are more prone to form melanomas... To read the complete article you need to be a subscriber
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