According to ATCOFA graduate student Julie Williams, humans are not the only species susceptible to skin cancer. Gray horses also are particularly vulnerable to the disease.
“Generally, 80 percent of gray horses will develop melanoma by age 15,” Williams said.
Gray horses are born in a variety of coat colors and progressively change to the color gray as they age. The same genetic factors that facilitate this change in coat color also are associated with a high incidence of melanoma in gray horses, Williams said.
According to Dr. Stacie Appleton, assistant professor of agriculture at SFA, equine melanoma typically appears as round, raised nodules that vary in size. The tumors appear most often near the nose and muzzle areas, as well as under the tail and between the back legs. Tumors also develop around and inside of the eye, as well as inside the ears, said Appleton. As with humans, the growths can be benign or malignant.
Under the direction of Appleton, Williams is investigating the possibility of mutations in the melanocortin-1 receptor of gray horses, which may provide insight into the prevalence of the disease, as well as treatment options.
In mammals, the melanocortin-1 receptor, or MC1R, regulates the type of melanin, or pigment, produced in skin and hair. Abnormalities in this gene have been associated with a high risk of melanoma development in humans.
“Gray horse melanoma and human malignant melanoma share a series of common features,” said Williams. “Inherited genetic variations affect risk and development (of skin cancer) in humans, and due to the similarities between humans and gray-horse melanomas this may be present in gray horses, as well.”
Williams is extracting DNA from blood samples of gray horses in order to amplify the MC1R gene for sequencing. Once the genes are sequenced, Williams will compare the gray-horse DNA to that of non-gray horses to determine if any polymorphisms, or specific mutations, exist in gray horse MC1R genes. If abnormalities are found, that knowledge could be used to further evaluate gray horses diagnosed with melanoma against those that have not developed the disease, Williams said.
“The capability to identify inherited variants of the gene could allow for identification and early detection of horses at an increased risk of developing melanoma,” Williams said.
Appleton added the identification of inherited gene variants also would be used to educate horse breeders, informing them of lineages that should not be crossed due to potential disease proliferation.
An in-depth examination of genetic mutations leading to equine melanoma is greatly needed, according to Appleton. In addition, she would like to extend Williams’ research to determine if early cancer detection tests used in humans could be applied to horses.
“Overall, a better understanding of the signaling mechanisms in horses and humans can result in new methods for the detection and treatment of melanoma in both species,” Williams said.
Dr. Stacie Appleton, right, SFA assistant professor of agriculture, stands with Eeyore,
a retired gray racehorse who calls the SFA Equine Center home. Pictured with Appleton is Michaelle Coker, SFA Equine Center supervisor.