NAVLE Integumentary

Equine Melanoma Study Guide

Equine melanoma is a tumor arising from abnormal proliferation of melanocytes, the pigment-producing cells of the skin. Unlike in humans, equine melanomas are not associated with ultraviolet light exposure.

Overview and Clinical Importance

Equine melanoma is a tumor arising from abnormal proliferation of melanocytes, the pigment-producing cells of the skin. Unlike in humans, equine melanomas are not associated with ultraviolet light exposure. Melanomas represent the third most common skin tumor in horses (after sarcoids and squamous cell carcinoma), with an incidence of approximately 80% in gray horses over 15 years of age. Understanding the genetics, classification, diagnosis, and treatment options is essential for NAVLE success.

High-YieldWhen you see 'gray horse' and 'black nodular mass under the tail' on the NAVLE, think melanoma first! Remember that up to 66% of equine melanomas may become malignant over time.
Coat Color Melanoma Risk Clinical Significance
Gray 80% by age 15 Most common; often multiple tumors; slower progression
Non-gray (Bay, Chestnut) Rare Usually single tumor; MORE AGGRESSIVE; higher malignancy rate

Etiology and Pathogenesis

Genetic Basis: The Gray Gene and STX17 Mutation

The development of melanoma in gray horses is linked to a 4.6-kb duplication in intron 6 of the Syntaxin 17 (STX17) gene. This same mutation causes the progressive graying of the coat. The gray gene is an autosomal dominant trait affecting chromosome region containing STX17, NR4A3, TXNDC4, and INVS genes.

Key genetic concepts for the NAVLE:

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