Equine melanoma

[1] Melanomas are the third most common type of skin cancer in horses, with sarcoids being the first most prevalent and squamous-cell carcinoma being second.

[2] Melanomas are typically rounded black nodules that vary in size and are usually found underneath the dock of the tail, in the anal, perianal and genital regions, on the perineum, lips, eyelids, and sometimes near the throatlatch.

Methods used to determine malignancy include fine needle aspirate, biopsy, or complete removal.

[4] To determine if the tumor has metastasized, a rectal examination or an ultrasound can be performed; the most frequent location for metastasis includes the lymph nodes, spleen, liver, abdominal wall, lungs, and blood vessels.

[5] The gray coat color is the result of an autosomal dominant trait that is caused by a 4.6-kb duplication in the 6th intron of the gene syntaxin-17 (STX17).

[7] The region of this mutation contains four genes: NR4A3 (nuclear receptor subfamily 4, group A, member 3), STX17, TXNDC4 (thioredoxin domain–containing-4¢) and INVS (inversin).

They are most commonly found in mature grey horses (less than 15 years old), typically under the tail, around the anus, and on the external genitalia.

They are most commonly found in gray horses over the age of 15 as a large coalescing mass under the tail, around the anus, on the external genitalia, or the parotid salivary gland.