Dermal malignant melanoma in a horse with multifocal pancytokeratin expression.

The research focuses on the discovery of a case of dermal malignant melanoma in a 13-year-old bay Thoroughbred mare, providing a rare instance of an equine melanoma demonstrating multifocal pancytokeratin expression.

Study Summary

• The study centers on a case of dermal malignant melanoma (skin cancer) discovered in a 13-year-old Thoroughbred mare. This case is especially remarkable because of its rare manifestation of multifocal pancytokeratin expression.

Microscopic Examination

• After a microscopic examination, it was observed that the cells of the tumor were arranged in cords and packets within an abundant collagenous stroma (a part of the connective tissue) that contained scattered myxomatous foci (areas of myxomatous degeneration, a change in the connective tissue).
• The tumor cells stained positive for S-100, neuron-specific enolase, and vimentin, indicating that the cells exhibited these substances or structures. Some cells even contained melanin granules, which are substances that give the skin its color and protect it from the sun’s harmful rays.

Pancytokeratin Expression

• Interestingly, some clusters of tumor cells were also positive for pancytokeratin – a type of keratin expressed in all epithelial (skin) cells. This is unusual as the expression of epithelial cell markers (like pancytokeratin) is rare in melanomas.
• While this feature has been described in a small number of human melanomas, its presence has never been reported in equine melanomas before. Therefore, this discovery contributes new knowledge to the study of equine melanomas and potentially broadens our understanding of the pathology of this disease.