Could another cancer vaccine be paving the road to victory for the “old gray mare” or other horses with melanomas? Pat Lawman, PhD, chief executive officer of Morphogenesis Inc., said a clinical study involving 30 horses with melanoma could help prove their vaccine is a viable treatment option.

Melanomas are among the most common skin tumors in horses. They are particularly common in gray horses because the gene responsible for the gray coat color is also responsible for melanomas. In fact, less than 6% of gray horses over the age of 16 are free from melanomas, which occur most frequently around the tail, anus, eyes, and lips.

Because current treatment strategies are limited and many are not curative, a small handful of researchers in this field have explored the potential for developing vaccines that can treat affected horses. One example is a vaccine directed against “tyrosinase,” a molecule present on melanoma cells.

Jeffrey Phillips, DVM, MS, PhD, Dipl. ACVIM, assistant professor of veterinary medicine at Lincoln Memorial University's College of Veterinary and Comparative Medicine, said one melanoma vaccine (trade name Oncept) has had a good response in their clinical trial. Specifically, the researchers inject 15 horses “with a series of four biweekly injections along with a six-month booster,” Phillips and colleagues wrote in an abstract summarizing their work, supported by the Morris Animal Foundation. In that study Phillips found that the tyrosinase vaccine “appears to be safe and well-tolerated in tumor-bearing horses and appears to result in both clinical activity and a measureable immune response