Melanomas are tumours frequently found in grey horses (Lipizzaners, Portuguese, etc.). They are often black pigmented but may also have no particular pigmentation.
These skin tumours are classically observed on the underside of the tail, in the perineal region, on the sexual mucosa, the lips, the udder, the peri-ophthalmic and parotid region.
Melanomas are often classified into 3 types according to histopathological characteristics and malignancy criteria
- Melanocytomas (melanoma nevi) are tumours located in the superficial dermis with invasion of the epidermis of the skin. More than 70% of melanocytomas occur in horses under 6 years of age of all colours. Most are found in atypical body sites. They are classically benign!
- Dermal melanomas are located a little deeper in the skin; in the deep dermis. This type of melanoma occurs in 80% of cases in horses over 6 years of age, often with a grey coat. They are found in the body areas classically described for equine melanomas. These tumours can metastasise and should be considered as potentially malignant.
- Anaplastic melanomas mainly affect horses over 20 years of age and without coat predisposition. This type of melanoma metastasises and is the most aggressive form of equine melanoma.
There are few medical treatments. The use of oral cimetidine has been documented but the results of this treatment vary according to published studies.
Surgery, when feasible, remains the recommended treatment for dermal melanoma.
Vaccines are currently under investigation but none are currently available on the market.