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%.
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• 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 •