Overview: Sarcoids are the most common skin tumor present in the horse and can vary in appearance. Sarcoids do not metastasize to internal organs, but are a challenge to treat. Sarcoids can be present anywhere, but are most common on the chest, groin, sheath, legs, underside of barrel and head. Many breeds are affected by sarcoids, but Quarter Horses are the most common.
Types of Sarcoids:
1. Occult- These sarcoids look like rough, hairless areas of skin and are often more subtle in appearance. These may resemble ringworm or ‘rub-marks’ from tack. These are common on the nose, the side of the face, armpit and groin.
2. Verrucous- These have a ‘wart-like’ appearance and are often grayish in color.
3. Nodular- These are firm and round in appearance. They can be ulcerative or have a layer of normal skin over them.
4. Fibroblastic- These are fleshy, ulcerative and often bleed easily. They look similar to ‘proud flesh’ and may even develop at the site of a wound. They can also develop from other ‘forms’ of sarcoids.
5. Malevolent- This is the most aggressive sarcoid and spreads in location and size very quickly. These will often look like bundles of ulcerative, nodular lesions. These are very difficult to treat, but are rarer than other types of sarcoids.
6. Mixed- combination of more than one type of sarcoid from above.
Diagnosis: The diagnosis is often based on the appearance of the tumor. In more difficult cases, a biopsy may be taken. However, a biopsy may trigger the sarcoid to grow and/or spread to other locations.
Treatment: Unfortunately, there are no great treatment options for sarcoids. They all respond differently to the many treatments available. Examples of treatment options include:
1. Benign neglect- This includes monitoring the sarcoid for changes in appearance or growth. This is often recommended for sarcoids that are not bothering the horse.
2. Surgical removal- Surgery must be done cautiously. The issue with removing sarcoids is that they often have many finger-like projections that grow into the skin and can be quit long making complete removal difficult. If a sarcoid is not removed in its entirety, it often returns and is usually more aggressive. It may also trigger sarcoid growth in other areas of the body. Decision to proceed with surgery will depend on the location and type of sarcoid.
3. Cryosurgery- Involves the use of liquid nitrogen to freeze the cells and prevent them from dividing. This is only effective on small, superficial lesions and has a high rate of reoccurrence.
4. Intralesional cisplatin injections- Cisplatin is a chemotherapy medication that can be injected directly into the sarcoid at 2 week intervals for 3-4 doses. The sarcoid will look worse before it looks better with this treatment due to inflammation.
5. Imiquimod (Aldara)- This is a cream that is an immune response modifier that is also used for skin cancer in humans. This is a cream that is applied over the sarcoid. Initially, the cream is applied 3 times per week and treatment often continues for 2-4 months. Again, the sarcoid often looks worse before it looks better due to inflammation. The cream may also cause the area to be painful.
6. Radiation therapy- this involves approximately 4 treatments one week apart. The horse will have to go to a referral facility that performs radiation such as The Ohio State University. The horse will also have to be placed under general anesthesia for a short period of time.
7. Xxterra- This is an herbal paste that alters the tumor in a way that the body recognizes it as ‘foreign’. It causes the tumor to slough off. This will also make the tumor appear worse before it gets better and the tumor can be sore to the touch. Treatment continues until the tumor sloughs.
Conclusion: Sarcoids can be difficult to treat and have a high chance of reoccurrence. There are no great treatment options for sarcoids and the response to a certain treatment modality will vary.
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