There are no guarantees that treatment will circumvent future health issues, particularly when it comes to squamous cell carcinoma (SCC)
—the most common ocular neoplasia (tumor) in horses. For many health conditions, veterinarians can use research study data to provide estimates of how likely a horse’s condition will return. But for SCC, that range is wide.
“Studies reported recurrence rates of 25% to 67%,” said Nicole Scherrer, DVM, at the 2018 American Association of Equine Practitioners Convention, held Dec. 1-5 in San Francisco, California. “We didn’t have a good number to give clients.”
Scherrer is a clinical assistant professor of ophthalmology at the University of Pennsylvania School of Veterinary Medicine (Penn Vet) New Bolton Center, in Kennett Square. Seeking to narrow recurrence estimate windows and identify which factors make it more likely, she conducted a retrospective study on 36 horses treated for eyelid SCC at Penn Vet from April 2002 through January 2018. She included horses that:
- Had a histologic (via microscope examination of a tissue sample) diagnosis of SCC;
- Underwent treatment; and
- Had been available for at least three months of follow-up checks.
Male horses made up 76% of the study population, and the median patient age was 14. Scherrer said Paint horses made up nearly three-quarters of the study population. Less-prevalent affected equids included Appaloosas, a cremello Tennessee Walking Horse, and a cremello mule.
Regarding the tumors, treatments, and recurrence rates, she found that
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- 55% of horses had an SCC on the right eye, 36% on the left, and 9% on both;
- SCCs were present on both the upper and lower eyelids in 44.5% of horses, on the lower only in another 44.5%, and on the upper only in 11%;
- SCC lesions ranged in size from 0.5 to 10 centimeters, with a median of 2 centimeters;
- Initial treatments included wedge resection (removing the lesion and shortening the eyelid margin—where the eyelashes are located), canthoplasty (surgery to restore the canthus, where the eyelids meet), resection plus canthoplasty, and H plasty (taking the skin from above or below the lesion and pulling it up to create a new eyelid margin); there were no significant differences in recurrence rates among surgical techniques;