Sarcoids
Basic Information 
Epidemiology
Genetics and Breed Predisposition
• Overall prevalence 0.5% to 2%; may be higher in some populations; most common skin neoplasm of horses.
• Although all breeds of horses are susceptible, some breed predispositions have been recognized. In the United States, sarcoids are relatively more common in Quarter Horses, Appaloosas, and Arabians and less common in Standardbreds.
• Genetic predispositions have been associated with specific equine leukocyte antigens.
Clinical Presentation
Disease Forms/Subtypes
• Six subtypes of sarcoids based on clinical appearance and biologic behavior
Occult: Mild cutaneous scaling and alopecia; most benign form; often remains quiescent with little change in appearance or growth
• All subtypes are capable of transforming to more malignant variants.
• A simplified classified system has been proposed based on tumor behavior
Physical Exam Findings
• Appearance varies with subtype.
• Lesions are typically firm and annular. They may be any size and are often poorly circumscribed. The appearance of the overlying skin is highly variable, ranging from normal to alopecic to ulcerated.
• Site predilection: Lesions can develop anywhere on the body, but some sites are more common.
• Sarcoids on the distal limb and periorbital region may have a worse prognosis than sarcoids at other sites.
Etiology and Pathophysiology
• Malignant transformation of cells may result from genetic and exogenous factors.
• BPV DNA has been found in nearly all equine sarcoid tissues examined.
• Behavior: Generally classified as benign but often locally invasive with a tendency to recur
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