Squamous cell carcinoma originating from an epithelial scar in a horse.

This study represents a case of a Quarter Horse stallion that developed squamous cell carcinoma, a type of skin cancer, in a fibrous scar that resulted from an abscess caused by an antihistamine injection.

Background and Objectives

• The instance centered on a scar that developed after an intramuscular injection of antihistamine triggered an abscess in a Quarter Horse stallion. This abscess healed, leaving significant fibrous scarring and persistent granulation tissue. The lesion remained static for two years, after which the granulated tissue began a six-month period of progressive enlargement.

Methods

• During this period, an excisional biopsy was performed on the lesion, leading to a histopathologic diagnosis—that is, a diagnosis made by microscopic examination of tissue samples—of squamous cell carcinoma, a type of skin cancer commonly associated with scarring, inflammation, and chronic injuries.

Findings

• The subsequent debilitation of the horse is outlined: Over six months following the diagnosis, the horse experienced a decrease in body weight and an increase in the diameter of the lesion.

Conclusion

• Deterioration of the horse’s physiological condition due to the carcinoma, led to the decision to euthanize the horse. This case exemplifies the potential for squamous cell carcinomas to originate from areas of the body that underwent significant scarring or chronic inflammation as a result of injury or infection, underscoring the need for constant surveillance of such areas in animals.