Melanomas

Veterinary advice should be sought before applying any treatment or vaccine.

Melanomas

Equine Malignant Melanoma, Equine Melanocytic Disease

Equine melanomas is a skin tumor of pigment producing cells, that is the most common tumor in aging grey horses worldwide. Melanomas can occur anywhere on the body of the horse however they are more frequently found along the tail base, anus, external genitals, throat latch, mouth, and the margin or outer part of the ear.

Melanomas may exist for many years without growing in size or causing any problems for the horse. However, once they begin to grow in size is when they can present a significant problem for the horse. If melanomas develop and enlarge in the throat latch area, they can cause horses to be unable to flex at the poll, turn their heads from side to side, or eat or drink comfortably. Geldings or stallions that develop melanomas in the sheath can cause discomfort for the horse to urinate or breed. Horse's with large melanoma growth on their anus or tail base can develop extreme intermittent discomfort when defecating.

Symptoms

Pigmented raised nodules

Diagnosis

  • History
  • Clinical signs
  • Physical examination
  • Biopsy

While waiting for your veterinarian

  • Regularly look over gray horses and identify any new or increase in size of existing melanomas

Treatment

TherapiesDetails
Xenogenic DNA vaccinationAn antigen-specific gene immunotherapy, using a Xenogenic DNA plasmid in the form of several by-weekly injections with a DNA-based vaccine to target an immune response against the melanoma protein tyrosinase. Clinical trials have been conducted on horses at the University of TN showing it to be a safe and well tolerated form of treatment. However it is a high cost treatment, starting at $2500 and up.
CimetidineA histamine H2-receptor antagonist that as a daily oral supplement, has had mixed results of effectiveness, but has been found in some horses to prolong survival of horses with melanomas, depending on the type and size of the melanomas.
CisplatinA heavy metal compound that inhibits DNA synthesis. It was reported be 81% effective in cases of early-stage melanomas that were not previously treated. However new tumors continued to develop in other areas of the body. Implanting cisplatin-containing biodegradable beads into the tumor alongside conventional debulking or CO2 laser debulking was found to be successful at resolution of tumors for at least 2 years following treatment.
Surgical excisionReport ably the most effective form of treatment for horses with stage 1 or 2 melanomas. However, in a study conducted by Rowe and Sullins in 2004, they discovered close to half of the horses in the study which had their tumors surgically removed ended up having that tumor increase in size or developed more tumors at the same location or elsewhere on the body.

Scientific Research

General Overviews

Clinical Trials

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Age Range

80% of older grey horses will develop melanomas by the time they are 15 years of age.

Risk Factors

  • Gray or white skin color

Commonly Affected Breeds

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