Squamous Cell Carcinoma – Skin Cancer in Horses

Most people who have been around horses long enough have probably heard that White horses are very susceptible to cancer. I recently found myself in the disheartening position of learning that my horse, Rio, had squamous cell carcinoma on his eyelid.

At first, I viewed the small bumps on his eyelid as harmless. However, I took pictures so that I could monitor the growth of these bumps. Luckily, just a short time later, during a routine vet appointment, the Vet pointed out that these bumps were potentially Squamous Cell Carcinoma, which is actually a form of skin cancer that can be fatal to your horse...if left untreated.

I was a bit shocked and disappointed because for the last few years, I have taken precautions to make sure that he had a good UV protective fly mask on whenever he was out in the sunlight…all year round. Some at the barn questioned why the mask in the middle of winter and I explained that we were protecting his face and eyes from sun damage. Apparently, it was not enough.

Shortly after diagnosis and discussions with the vet, Rio was scheduled for surgery where the doctors were able to remove the bumps. They also found 2 additional bumps on the other eyelid and third eyelid which we hadn’t even seen.

Thankfully, we caught it early and got it treated, so the surgery and recover were fairly simple.

What is Squamous Cell Carcinoma (SCC)

Simply put, it’s a form a skin cancer.

According to Equimed.com, SCC tumors appear as solitary, raised, irregular masses, often ulcerated or infected, that develop around the eyelids (and third eyelids), genitals, face and ears, anal region, and other areas with minimal hair coverage and pigmentation. SCC tumors are slow-growing and are found most often in horses with white faces or markings that extend around the eyes.

According to Practicalhorsemanmag.com, as it grows, squamous cell carcinoma can begin to invade surrounding tissues, including the eye or even bone. It can also metastasize to other parts of the body. 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.




On the skin, a squamous cell growth may look like a small sore or a red, raised bump. Small growths are often easy to spot when they appear around the eyes, where they're often on the inner rim of a lid or in the third eyelid (the membrane at the inner corner of the eye). Tumors in other spots, like the sheath, are more easily missed--look for red, raised sores and sometimes a foul odor.

Other symptoms may include:

  • Small nodules
  • Ulcerated areas with a foul odor
  • Loss of appetite
  • Weight loss
  • Lethargy
  • Abnormal chewing and swallowing behavior
  • Anemia


The skin form is typically treated by surgery combined with follow-up treatment.

According to Practicalhorsemanmag.com,

  • In surgery, the tumor is cut out along with some surrounding tissue and sent to a lab for analysis. The lab will confirm what it is and determine if the surgery got the entire growth.
  • If the tumor can't be surgically removed (it's in a difficult place, for example), chemotherapy may be an option. The growths can be injected with a cytotoxic (cell-killing) drug such as cisplatin. Those around the sheath can be treated with a topical drug.
  • Squamous cell carcinoma also can be treated with radiation. In one method, radioactive "seeds" are implanted in the tumor and left in place for a few days to destroy the abnormal tissue.
  • Cryotherapy (freezing) is sometimes used for small external growths.

Causes and Prevention

As with other types of skin cancer, primary causes of SCC is exposure from the sun’s UV rays. It’s especially common in unpigmented skin because there is poor protection from the sun and the harmful UV rays.

Although there is no way to completely prevent the occurrence of SCC, you should take steps to help lessen the chances and severity of the damage.

  • Protect horses with pink skin on the face or other areas from the sun as much as possible. Choose night-time turn out and keep faces covered with a good UV-rated fly mask any time the horse is in the sunlight.
  • Use sunscreen on unprotected areas if your horse does not have access or refuses to stay in the shade on sunny days
  • Clean gelding’s sheath regularly in order to prevent buildup of dirt and smegma and also to check for any bumps that may arise.
  • Check light-skinned areas regularly and thoroughly to catch this cancer while it’s treatable. This includes eyes, face, lips, nostrils, anus, and genital areas.

Early detection and treatment is the key to treating and preventing serious damage or further health risks. If you find any suspect bumps or skin irritation that does not heal on the areas mentioned above, definitely consult with your veterinarian as quickly as possible.

Here are a some of recommendations for good UV protective Fly Masks.  I've used all 3 and they are all of really good quality.

Guardian Horse Masks - 95% Sunshade  http://www.horsemask.com/

Equine Sunvisor - Advertised as 99.5% UV Block - http://www.equinesunvisor.com/

Prestige Fly Masks - UV Resistant up to 80% - http://www.prestigehorseflymasks.com/store/index.html


For more information on Squamous Cell Carcinoma, you can consult the following articles:

Squamous Cell Carcinoma, Equimed.com

Equine Cancer: Squamous Cell Carcinoma, Practicalhorsemanmag.com https://practicalhorsemanmag.com/health-archive/equine_squamous_cell_carcinoma_020910-11482

Squamous Cell Carcinoma in Horses, Wagwalking.com


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