Limbal squamous cell carcinoma in a Rocky Mountain Horse: Case report and investigation of genetic contribution.

This study documents a rare case of limbal squamous cell carcinoma (SCC), a kind of eye cancer, in a Rocky Mountain Horse, which also possessed a genetic risk factor (DDB2 c.1013C>T) known to contribute to this disease. In a larger group of the same breed, the frequency of this risk factor was found to be 20%. Further research is recommended to ascertain if there’s a significant link between this cancer type and the genetic variant among Rocky Mountain Horses.

Case Study Findings

• A mass affecting the right eye of a Rocky Mountain Horse stallion was examined. Suspected as limbal SCC, two common eye treatments, keratoconjunctivectomy, and strontium irradiation, were carried out.
• Confirmation of the disease was done via histopathology, a study of abnormal tissue change.
• An allelic-specific polymerase chain reaction (PCR) assay was performed on the horse’s DNA, isolated from its whole blood and hair follicles. This test ascertained that the horse was homozygous (having two identical forms of a specific gene) for the DDB2 c.1013C >T risk variant. This genetic variant is known to be associated with a higher risk of developing limbal SCC.

Population Study Findings

• A population study was conducted on 84 Rocky Mountain Horses to understand the frequency of this genetic risk variant.
• It was found that the frequency of the DDB2 c.1013C >T risk variant was 0.20, meaning that 20% of the examined population carried this genetic risk variant.

Study Conclusions and Recommendations

• The study concluded that the Rocky Mountain Horse breed has the DDB2 genetic variant, which has been identified as a significant risk factor for ocular SCC in Haflinger and Belgian horse breeds.
• It is recommended that further research, involving genotyping additional Rocky Mountain Horses diagnosed with ocular SCC and healthy controls, should be undertaken. This will help evaluate if a significant connection exists between ocular SCC and the DDB2 c.1013C >T risk variant in the Rocky Mountain Horse breed.