Texas Equine Veterinary Association

www.texasequineva.com • Page 8 LESLIE EASTERWOOD, DVM Texas A&M University Veterinary Teaching Hospital Periocular squamous cell carcinomas of white skin of the eyelids can be a very frustrating condition leading to loss of lid function and potentially the globe. If noticed and treated early, there are many treatment options available. The best option is highly dependent on the structures involved and extent of the involvement. Frequently owners do not seek treatment for periocular SCC until the tumor is large enough and invasive enough that enucleation is the best option to remove enough tissue to achieve reasonable assurances of tumor resolution with clean margins. Loss of integrity of the remaining lid can also lead to eyelid dysfunction and an inability to lubricate the globe adequately. In this case, enucleation would be the only viable option. There are many adjunctive treatment options to combine with debulking of the tumor. Cryotherapy, injectable chemotherapy, topical chemotherapy, and hyperthermia have been reported with variable success rates. H-plasty can be successful in some instances to achieve clean margins of a lid tumor, but can have limitations if the tumor involves too much length of the lid margin. The use of photodynamic dye therapy for squamous cell carcinoma has been described in humans and small animals. In these cases, the dye is injected systemically, and the tumor is then exposed to the appropriate light wavelength percutaneously for a deep tumor, or directly for a surface tumor. For the larger species, however, the dose is injected directly into the tumor bed after the majority of the tumor is debulked. The tumor bed is then exposed to the appropriate wavelength to activate the dye. For PDT in horses, with standing sedation, the tumor is debulked down to surface level, without trying to get a completely clean margin. The goal is to get the tumor bed flat and have enough U S E O F P H O T O D Y N A M I C D Y E T H E R A P Y F O R PERIOCULAR SCC remaining tissue to be able to retain the dye. The dye is injected into the tumor bed based on surface area of the site. With the globe protected with a Styrofoam shield covered in duct tape, a 680nm visible red light is used to activate the dye within the tumor bed. Remodeling of the tumor bed can take up to four months, and requires periodic rechecks and possible adjunctive therapy for complete resolution. The average reoccurrence rate after cryotherapy is nine months, whereas published periocular SCC cases treated with PDT had no reoccurrence after 60 months. Photodynamic dye therapy is an emerging option for invasive periocular SCC. Costs are variable depending on size and nature of the tumor, but PDT generally runs $850–1000 for the initial treatment. Photodynamic dye therapy should be most successful if used for smaller lesions early in the process of lid margin invasion, but can also be considered for more extensive lesions as an alternative to enucleation. References: Giuliano, et. al., Photodynamic Therapy for the treatment of periocular squamous cell carcinoma in horses: a pilot study. Veterinary Ophthalmology, vol 11, 27–34.

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