Study: Surgery, Chemo Preferred Combo For Treating Squamous Cell Carcinoma

A horse's nictitating membrane, sometimes called the “third eyelid,” is a thin layer of tissue that covers the eye as the horse blinks. Its purpose is to moisten the eyeball and keep dirt and debris out.

This membrane can sometimes develop tumors caused by squamous cell carcinoma (SCC). It is often in the best interest of the horse to address these tumors so they don't interfere with the horse's health, reports EQUUS magazine.

To determine the best therapy for SCC, researchers at the University of Pennsylvania's New Bolton Center studied the records of 50 horses treated at the hospital for masses on their nictitating membranes.

They determined that 45 of the masses on the nictitating membrane were abnormal growths, and 37 of the masses were squamous cell carcinoma. Nineteen of the horses were treated with partial or complete surgical removal of the nictitating membrane as the sole therapy. The other 31 horses had surgery that was followed by topical chemotherapy.

Reports following the surgery showed that the masses recurred in 20 percent of study horses, with the average time to recurrence being two years and three months. Chemotherapy use did not have a significant effect on the recurrence rate, but five horses that were given a specific type of chemo had no recurrence.

Follow up reports showed that six of the horses were euthanized because of poor quality of life due to persistent discharge, obstruction of airflow or deformation of bone.

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When a horse arrived at New Bolton with a portion of his eyelid already removed, the risk of mortality was significantly higher than those horses that did not have surgery prior to being referred.

The researchers concluded that surgical removal of the eyelid in its entirety is recommended rather than simply performing a biopsy on the mass. Surgical removal followed by topical chemotherapy is the treatment of choice by New Bolton veterinarians.