In a previous study, researchers found about 26% of SCC-affected horses in a retrospective study were Haflingers.

Genetic Link to Equine Eye Cancer Found

Squamous Cell Carcinoma

Researchers have identified a genetic mutation in horses allowing for the identification of horses at risk for squamous cell carcinoma of the eye.

Squamous cell carcinoma (SCC) is the most common cancer found in equine eyes. It is the second most common tumor of the horse overall, according to researchers.

A recent study led by UC Davis allows horse owners to identify horses at risk for ocular SCC and make more informed breeding decisions. Scientists announced the discovery of the genetic mutation in horses in the International Journal of Cancer.

Ocular SCC can lead to vision loss or loss of the eye. In advanced cases, SCC can become invasive locally. It then spreads to the orbit, eating away at the bone and eventually the brain, which can cost the horse its life.
photo by UC Davis

Several equine breeds, including Haflingers, have a higher rate of what is called ‘limbal SCC’. It originates between the cornea — the clear surface of the eyeball — and the conjunctiva that covers the white of the eye. In a previous study, researchers found about 26% of SCC-affected horses in a retrospective study were Haflingers.

“The fact that we see this type of cancer in a relatively small breed with a narrow pedigree makes it a good model to study,” researcher Mary Lassaline, DVM, Ph.D., MA, DACVO said.

Ocular SCC can lead to vision loss or loss of the eye. In advanced cases, SCC can become invasive locally. It then spreads to the orbit, eating away at the bone and eventually the brain, which can cost the horse its life.

“One, it’s important for the individual horse with a known risk and we can be more vigilant about exams as well as protecting their eyes from UV exposure,” Lassaline, associate professor of clinical equine ophthalmology at the UC Davis Scool of Veterinary Medicine adds. “If detected early, we can remove the tumor and save the eye.”

Scientists at the UC Davis Veterinary Genetic Laboratory also developed a genetic test for horses. It determines if a horse carries the mutated gene or has two copies of the risk variant. Both put horses at the highest risk for cancer.

The study may have implications for humans as well.

The gene associated with equine SCC is also linked to a disease in humans (xeroderma pigmentosum complementation group E). It is characterized by sun sensitivity and increased risk of cutaneous SCC and melanoma.