Squamous Cell Carcinoma in Horses

Squamous cell carcinomas start out as small, red bumps that can be barely noticed on areas of unpigmented skin. These bumps may seem harmless, but they are actually a form of skin cancer that can be fatal to your horse. If you find an abnormal lump, a skin irritation that does not heal, or if your horse is showing changes in behavior, the sooner you get your veterinarian involved the better. Squamous cell carcinomas will grow and possibly metastasize to other parts of your horse’s system. Surgical removal, as well as therapies such as radiation and chemotherapy, can be utilized in the treatment of this condition. The earlier the treatment begins, the better your horse’s prognosis of recovery is.

Squamous cell carcinomas are one of the most common types of skin tumors found in horses. These appear most commonly in the eye, on the genitalia or in other areas of unpigmented skin. If you notice an abnormal bump or growth on your horse, call your veterinarian immediately for a consultation.

Symptoms may start out as barely noticeable and then develop into secondary complications. Symptoms may include:

• Small sore
• Raised bump
• Foul odor
• Noisy breathing
• Lack of appetite
• Ocular discharge
• Bleeding from the penis
• Difficulty urinating or defecating 

Bumps develop most commonly on places of the body where mucous membranes meet the skin. 

Types

The most common types of skin tumors in horses include sarcoids, melanomas, and squamous cell carcinomas. Squamous cell carcinomas can be ulcerative or proliferative masses found most commonly in unpigmented areas of skin. Tumors will start out small, but can grow very quickly if not caught and treated.

Squamous cell carcinomas first appear where the mucous membranes meet the skin. These places also happen to be unpigmented skin that has very poor protection from the sun’s UV rays, a major factor of the cause. As the tumor grows, it can spread to the lymph nodes and then metastasize to other parts of the body. The location of the tumor can lead to unusual symptoms not seen in the most typical cases.

Your veterinarian will want to do a full physical on your horse. As an example, while the tumor may obviously be in his eye conjunctiva, the veterinarian will want to check the rest of his body for other tumors. Your veterinarian may want to take a biopsy sample for testing in order to appropriately diagnose what type of tumor it is. If there are other areas being affected by similar tumors, she may want to collect samples of those as well.

If she believes the tumors have metastasized, your veterinarian may want to take a chest radiograph to check your horse’s lungs. If the tumors have metastasized to his lungs, it will help the veterinarian determine her course of treatment. If your horse is experiencing a lack of appetite, she will also want to check his GI system for tumors as well. 

Blood work will be conducted to see if the internal organs are functioning properly. The blood work will also show how your horse’s body is responding to the tumors and whether he will need additional therapies added to his treatment regimen.

Treatment for your horse will have multiple variables. The location of the tumor and economic concerns will play a large role. Surgical removal is a common form of treatment of squamous cell carcinomas in horses. Additional therapies may also be utilized at the same time of surgical removal to ensure the entire tumor was removed. Cryotherapy, laser therapy, photodynamic therapy, brachytherapy, radiation and chemotherapy can be used in conjunction with surgery. 

Follow up treatments, such as cisplatin injections, will need to be done after surgical removal of the main tumors. Since squamous cell carcinomas tend to recur, your veterinarian may need to cut and inject the area multiple times to ensure the tumor has been completely removed. If you do not do the follow up treatments properly or wait too long, you may have to start the entire treatment process over or your horse may never properly recover.

Early diagnosis is important when it comes to squamous cell carcinomas. If recognition is delayed and therefore causes treatment to be delayed, the chance of recurrence and metastasis increases. If the condition is caught early and treatments are started quickly, prognosis of recovery is good. However, if it is left untreated and allowed to metastasize to other areas of the body, your horse’s prognosis declines greatly and the condition can even lead to his death.