Pigmented squamous cell carcinoma of the conjunctiva of a horse.

The study involves a unique case of a heavily pigmented tumor found in a specific part of a Thoroughbred horse’s eye, initially suspected to be a melanoma but discovered to be a pigmented squamous cell carcinoma (SCC) after testing. This is considered to be the first documented case of a pigmented SCC in a horse’s eye in veterinary research.

Investigation and Identification

• The study centers around a Thoroughbred horse with a deep-colored tumor removed from the lateral, perilimbal, bulbar conjunctiva, a specific area of the horse’s eye.
• Initial assumptions pointed towards the tumor being a melanoma, a common type of skin cancer known for its black or brown pigmentation. This led the team to perform a laser surgery on the base of the tumor after its excision.
• Following the surgery, the horse demonstrated no other symptoms or signs related to ophthalmic lesions.
• A histological examination was conducted, which involves studying the microscopic structure of the tissues. This test revealed that the removed tumor was not a melanoma, but a pigmented squamous cell carcinoma (SCC).

Pigmented Squamous Cell Carcinoma (SCC)

• SCC is a common type of skin cancer derived from squamous cells, the cells that make up the outer layer of the skin.
• SCCs are usually not pigmented; thus, having a pigmented variety is unusual and is what makes this case noteworthy. SCCs often appear as scaly patches, open sores, red elevated nodules, or growths with a central depression; on rare occasions, they can show pigmentation.

Implications

• The prognoses and treatment protocols for SCC and melanoma are different, which highlights the importance of this misdiagnosis. It shows the need for accurate diagnosis which can lead to more effective treatment suggestions.
• According to the authors, this is the first reported case of an ocular pigmented SCC in a horse in veterinary literature, making it a significant contribution to field knowledge and further research.