What The Muck Is That? Squamous Cell Carcinoma

Amanda Uechi Ronan details this common skin tumor, and Kristen Kovatch shares her firsthand experience in treating this equine disease.

Randy’s squamous cell carcinoma in April 2016. All photos by Kristen Kovatch.

The American College of Veterinary Surgeons tells us the three most common types of skin tumors in horses are:

• Sarcoids
• Melanomas
• Squamous Cell Carcinoma

Most equestrians are familiar with melanomas — found on greys under the tail, around the anus, around the eyelids, at the throat latch and on the sheath — and sarcoids — the most commonly recognized skin tumor in horses which is thought to be viral — but fewer people have heard about squamous cell carcinoma.

Squamous cell carcinomas are the “most common malignant skin tumor in horses” (Merck) and are usually found in adult to geriatric horses. They look like proud flesh and are most commonly found on un-pigmented areas of skin, such as around the eye and urinary and genital organs. Breeds most affected are Appaloosas, Paints and some draft breeds. The number one causative factor appears to be UV damage.

Dr. Eades told Practical Horseman, “Growths around the eyes may spread first to the lymph nodes under the jaw. Once in the lymph system, the cancer can travel to other locations. It’s the most common internal tumor in the intestinal tract, and the second most common overall.”

Thankfully, with proper treatment, the outlook is very good for horses with this type of cancer.

Signs To Look For:

• Small sores or red, raised bumps
• Occasionally a foul odor
• In the sinuses or upper throat, tumors can cause noisy breathing.
• In the esophagus or the stomach, the horse will have problems in eating.

Keys to Prevention:

• Give horses with pink skin extra protection from the sun. Night turn out and fly masks with UV protection are highly recommended.
• Clean a gelding’s sheath regularly. Not only for diagnostic purposes, but some contribute the buildup of dirt and smegma to a higher likelihood of contracting cancer.
• First and foremost, check your horses light colored skin regularly.

Treatment Options:

Surgery, chemotherapy, radiation and cryotherapy are all options for treating SCC, but surgery with follow-up Cisplatin injections is generally the preferred treatment plan.

Horse Nation’s managing editor Kristen Kovatch recently dealt first-hand with squamous cell carcinoma and shares her experience:

My adopted draft horses Rocky and Randy are Belgians, a breed predisposed to developing squamous cell carcinoma. I had been forewarned that Randy had a growth on his left eye when I brought them home, and promptly made an appointment with the Cleveland Equine Clinic of Ravenna, Ohio to have the growth removed. (Rocky came along as well for a preventative eye exam, and also so that he did not tear the farm down while his partner was away.)

Randy’s symptoms first presented as a weepy eye and the third eyelid looked inflamed, as though he had something stuck in it. The tumor itself grew over the course of several years but most recently had grown particularly quickly over about six months. Dr. Hill of CEC noted that in an ideal situation she would have liked to have removed the growth when it was a good deal smaller; when she pressed back Randy’s eyelids to show us the extent of the SCC I was shocked to see how much of the third eyelid was actually growth. She estimated that in a few more months it would have been too large to remove.

The procedure itself was done standing; Randy was sedated and then locally anesthetized so that the third eyelid could be removed. Dr. Hill worked on the larger tumor first on Randy’s left eye; she estimated about 75% of the eyelid was malignant growth. He had a smaller SCC in his right eye which she also removed.

Click any image below to open the photo gallery. Due to the nature of the procedure, some of these images may be considered graphic!

Randy’s aftercare was fairly basic, considering the procedure: we administered IV Banamine for three days to help with lingering pain, he was put on SMZ for five days, we treated the left eye with triple antibiotic and he was placed on stall rest for a few days. Ongoing aftercare includes wearing a UV-blocking fly mask essentially for the rest of his life, including clear days in the winter.

Now, a few weeks later, it’s almost impossible to tell that Randy’s ever had squamous cell carcinoma. As he’s now without third eyelids, we do need to pay careful attention to his eyes to make sure that they are still cleaning and flushing properly, but so far all seems well.

Top photo: Randy in April 2016. Bottom photo: Randy, five days after surgery in June. The remainder of his third eyelid had not yet fully receded at this point but the absence of the tumor is striking.

My advice for all horse owners, especially those who own a breed or individual susceptible to SCC, is to take preventative action: much like you wouldn’t go outside all day in the summer without using sunscreen, protect your horses from the sun as well. My individual horses live out 24/7, which is an arrangement I’m not interested in changing, but if you have a part-time turnout animal, consider turning him out at night. Invest in UV-blocking fly masks. And don’t mess around with ocular health in particular: if you notice anything suspect going on in your horse’s eyes, don’t hesitate to contact your veterinarian!

Rocky and Randy sporting their brand-new UV-blocking fly masks.