Sarcoids

Sarcoids are the most common skin tumours in horses and ponies. Although they are benign and do not metastasize to the organs, they can be very aggressive locally. These tumours are associated with the bovine papilloma virus. The transmission of this virus can occur between cattle and horses or between horses, presumably via insects. Any horse can develop sarcoids, regardless of breed, age, or coat color. Even donkeys and zebras can be susceptible. However, some horses are genetically predisposed. Sarcoids can spontaneously develop or grow at poorly healing wounds. These tumours can develop anywhere on the body, but they are most commonly found in areas with thin, sparsely haired skin between the hind legs, around the udder and sheath, around the navel, in the armpits, on the eyelids, and around the mouth.

Diagnosis

The diagnosis of sarcoids can often be made based on their appearance. The lesions can be solitary, or multiple lesions can develop. Their appearance and size are highly variable.

We can distinguish between different types of sarcoids:

• Verrucous sarcoids: These sarcoids resemble warts and have a hyperkeratotic upper layer. These sarcoids are usually not very active.
• Occult sarcoids: These sarcoids appear as a small round, hairless spot with a grayish surface. These sarcoids are usually not very active.
• Nodular sarcoids: These sarcoids are located under the skin. The skin over the sarcoid appears macroscopically unaffected or may show alopecia. These tumours are often movable under the skin or may be attached to the skin.
• Fibroblastic sarcoids: These sarcoids appear as a tissue-like mass with an ulcerative surface. The surface of these sarcoids can easily become secondarily infected or infested with maggots. These sarcoids grow rapidly and are very infiltrative.
• Mixed type: Different types of sarcoids can occur simultaneously.
• Malignant type: These sarcoids are malignant and can spread to other parts of the body (only the skin). This type is often very aggressive and difficult to treat. Fortunately, this type is very rare.

An alternative option is to take a scraping/biopsy for histological examination or to detect the bovine papilloma virus with PCR. Care should be taken when taking biopsies as the tumour can be activated by this.

Treatment

The treatment of sarcoids can be very challenging. If sarcoids are unsuccessfully treated, they often become more aggressive and difficult to treat. Due to their infiltrative nature in the surrounding tissues, these tumours easily recur. Therefore, an appropriate treatment is necessary depending on the type of sarcoid, its size, and location. Sarcoids are best treated at an early stage, as the chance of complete healing is greatest. The larger and more aggressive the sarcoid, the greater the chance of recurrence. When the severity of sarcoids is ignored, they can become extremely large, making treatment difficult or even impossible.

Topical treatment

Small occult and verrucous sarcoids can remain stable for years or disappear on their own. Treatment with Efudix or Aldara may be indicated in these cases. Efudix is a cream based on 5-fluorouracil, which has a cytostatic effect. It will stop tumour growth, causing the tumour to die. The downside of this cream is that it causes a burning sensation, making the application of this cream difficult or even dangerous after a few treatments.

Aldara is a cream based on imiquimod, which causes a local immune response. This promotes the "clearing of abnormal cells," allowing the body to break down the tumour itself. This cream is less aggressive than Efudix and can therefore be applied more easily to sensitive areas (e.g., between the hind legs, around the udder). However, treatment with Aldara takes longer. These sarcoids should be closely monitored as they can change type and grow rapidly at any time. If this happens, immediate intervention is necessary.

Surgical excision

For some small sarcoids, surgical excision is a good option. The sarcoid is cut out with a wide margin. If the sarcoid is too large to close the skin primarily, excision with a laser can be chosen. In this case, the sarcoid is essentially burned away, and the wound is left open. After excision, the wounds must be closely monitored, as there is always a chance of recurrence. If this happens, quick intervention is necessary.

Tumour-specific electroporation (TSE)

Tumour-specific electroporation is a new treatment method for sarcoids with very good results (success rate up to 97%! for tumours smaller than 5 cm). In this therapy, the tumour is locally injected with a cytostatic product (cisplatin), which stops the DNA synthesis of the tumour. This causes the tumour to die. The action of cisplatin is therefore inside the cell. Since cisplatin is a large molecule and cannot easily penetrate the cell membrane, electrical pulses are given at the tumour site to depolarize the cell membrane (electroporation). This allows the cisplatin to act directly on the DNA synthesis, making the treatment much more effective. This also ensures that the cisplatin only has a local effect, which does not affect the horse's health. At Equitom, we have the latest technology, where in most cases this treatment can be performed while standing.

This treatment can be very useful for sarcoids where surgical excision with a wide margin is not possible (e.g., at the upper eyelid, large sarcoids), or for the treatment of aggressive sarcoids (e.g., fibroblastic form). It is also highly recommended for the treatment of extensive verrucous or occult lesions. Depending on the type of tumour and its size, 2 to even 8 treatments are needed to achieve complete regression of the tumour. The different treatments are always carried out at 3-4 week intervals.