Equine Health Update Issue 2 Volume 19 - Page 30

EQUINE | CPD Squamous Cell Carcinoma in Horses By Dr Rick Last – BVSc; M.Med.Vet (Pathology) Specialist Veterinary Pathologist, Vetdiagnostix – Veterinary Pathology Services Introduction Treatment S quamous cell carcinoma (SCC) is a common neoplasia of equines most often affecting the skin, eyes and genitalia, although a number of cases also affect the oral cavity, guttural pouch- es, stomach, and urinary bladder. Surgical resection forms the basis of treatment espe- cially where primary wound closure is possible. Surgical margins should be a minimum of 1cm. If complete local excision cannot be achieved then adjunctive therapy is required and includes Cutaneous SCC • Local Chemotherapy (Topical / Intra-Lesional) Fluorouracil based creams are commonly used topical chemotherapeutic agents. They are usually applied daily or every other day for 3–5 treatments. These agents are most effective in mitotically active lesions and so de- bulking surgery or laser debridement is advised before use. Intra-lesional cisplatin (injectable suspension or absorbable beads) is the most common locally applied chemotherapeutic agent used in the horse. Cutaneous squamous cell carcinomas are the most common malignant skin tumors of horses. Tumors arise from regions in the outer root sheath of the hair follicle. Neoplasms are most commonly documented in non-pigmented, sparsely haired areas of skin near muco-cutaneous junctions. Eyes, lips, nose, anus, and external genitalia (especially sheath around penis) are the most common sites. Breeds at increased risk are Belgian, Clydesdale, Shire, Appaloosa, American Paint, Draft horses, Quarter horses and Pinto. Chronic sunlight exposure, lack of pigmentation and thin haircoat are important predisposing factors, while cutaneous papillomavirus infection has been identi- fied as a contributing factor in some cases, particularly those tumours involving pigmented skin. Burn scars and chronic non-healing wounds are also predisposing factors to cutaneous SCC. Metastatic rates of cutaneous tumours are reported at ±18%. 30 • Cryosurgery Cryosurgery is usually applied with a thermocouple in place to monitor the temperature and depth of the freeze. Generally, three freeze and thaw cycles are used including normal tissue within 1 cm of the tumor to re- duce the risk of recurrence. Post-treatment complica- tions include local swelling, hyperemia, hemorrhage, edema and scar tissue contraction or blemishes may also occur with white hairs at the treated site. • Hyperthermia • Equine Health Update •