Equine Sarcoid Treatment Research

Research showed that a specific immunotherapeutic approach was applicable to any sarcoid, but it was particularly helpful for sarcoids not amenable to surgical excision.
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sarcoid horse ear

Cutaneous sarcoids come in a variety of different forms and often occur in areas that are difficult to access for surgical excision, such as around the eyes, head, face and ears (shown above).

Cutaneous sarcoids come in a variety of different forms and often occur in areas that are difficult to access for surgical excision, such as around the eyes, head and face. Historically, immunotherapy using a cell wall fraction of Mycobacterium phlei (Regressin by Bioniche) was used to stimulate an immune response by injecting the material directly into the tumor with several applications. An improved reformulation (Immunocidin® Equine by Novavive Inc.) of the original material is now being used for the same objective. This newer product is a veterinary biologic containing mycobacterium cell wall fraction and purified fragments of the Mycobacterium phlei cell wall. Mycobacterial cell complexes are known for inducing cytokine synthesis and apoptosis along with activation of immune cells such as T-lymphocytes.

The study enrolled 17 horses aged 4-23 years with confirmed histologic diagnosis of equine sarcoid based on punch biopsies [Caston, S.S.; Sponseller, B.A.; Dembek, K.A.; Hostetter, J.M. Evaluation of locally injected Mycobacterium cell wall fraction in horses with sarcoids. Journal of Equine Veterinary Science 2020; doi.org/10.1016/j.jevs.2020.103102].

The tumors were treated every two weeks with 2-5 injections of Immunocidin using a volume relative to tumor size based on manufacturer’s recommendations, at an average of 4.6 ml. Swelling developed in or around all injection sites within 24-48 hours following treatment. While the transient swelling resolved relatively quickly in most cases, a few took months to do so. In this study, NSAIDs were not given prior to treatment, but they were advised if there was significant swelling or soreness.

Follow-up of tumor response in the study was attained over 4-17 months. The authors stated that 2-5 treatments with Immunocidin Equine achieved nearly 53% regression.

  • Of 17 tumors, 9 resolved completely – 52.9%
  • Three improved to a smaller size - 17.6%
  • Three masses grew larger or showed no resolution – 17.6%
  • Of one horse with 2 masses, one resolved while the other developed a small growth five months after the final treatment.
  • One case was lost to follow-up.

No horses experienced any adverse effects other than mild to moderate swelling. This immunotherapeutic approach is applicable to any sarcoid, but it is particularly helpful for sarcoids not amenable to surgical excision.

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