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From The Ivory Tower | Ocular Squamous Cell Carcinoma
Squamous cell carcinoma (SCC) is the most common neoplasm of the equine eye and adnexa, frequently involving the cornea or corneolimbal junction, the third eyelid, and/or the eyelids. The incidence of periocular (located around the eye) SCC is related to increased age, poor skin pigmentation, and increased ultraviolet light exposure. Appaloosas, paints, pintos, Haﬂingers, and draft horses (Belgians, Shires, and Clydesdales) are at an increased risk of developing this disease. Approximately 30% of periocular SCC are located at the junction of the cornea (clear part of the eye) and the sclera (white part of the eye). This location is called the corneolimbal junction. The most common sites are the lateral (outside cornea of the eye) corneolimbal area and extending to the adjacent conjunctiva (thin, delicate tissue over the white part of the eye) and cornea.
Early signs of the disease may appear as increased redness of the cornea or conjunctiva, while progressive forms are typically white-to-pink with raised cobblestone architecture. Less commonly, SCC can actually invade the cornea and appear as a flat, spreading lesion extending throughout the corneal stroma. Deﬁnitive diagnosis of corneolimbal SCC requires taking a biopsy of the lesions and submitted it to the pathology laboratory; however, inspection of lesions in combination with identiﬁcation of predisposing factors (breed, poor skin pigmentation) is typically sufﬁcient for a presumptive diagnosis.
Treatment options reported for corneolimbal SCC in horses frequently involve surgical removal with additional therapeutic modality, such as cryotherapy, radiofrequency hyperthermia, β-irradiation, CO2 laser ablation, or topical chemotherapy with mitomycin C (MMC). Non-recurrence rates (how often we can remove/treat the cancer and NOT have it return) with the various therapies range widely from 45% to 100%; however, some form of additional therapy following surgical removal appears necessary as a means to decrease tumor recurrence. The particular therapy selected is based on the availability of equipment, ﬁnancial expense incurred, and necessity of general anesthesia vs. sedation when performing speciﬁc procedures, indicating that multiple options are necessary to most effectively and efﬁciently tailor treatment to the individual case.
What can you do to help your horse?
• Do a visual inspection of your horse’s eyelids and eyes on a routine basis.
• Become familiar with what is “normal” for your horse and contact a vet if you have any questions.
• If you notice a change in your horse’s eye, such as increase redness, squinting, or tearing, call your vet
immediately – any change in eye comfort or abnormal symptoms necessitates immediate evaluation.
• Although no formal studies have been conducted, using a fly mask may help to reduce risk of periocular
SCC by reducing ultraviolet light exposure.
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