Melanoma

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

Melanoma

Equine Malignant Melanoma, Equine Melanocytic Disease

Equine melanoma is a common type of skin cancer seen primarily in older, grey horses (over 8 to 10 years of age). In one study, up to 80% of grey horses over 15 years of age had developed melanoma. Melanomas are especially common in the Lipizzaner, Percheron, and Arabian horse breeds.

Melanomas can occur anywhere on the horse's body, however they are most frequently located at the perineum, the base of the tail, neck, mouth, eyelids, and mane. Other common locations include the parotid lymph nodes and salivary glands.
Tumors often involve multiple pedunculated nodules. Growths can also develop in internal organs. The majority of equine melanomas grow slowly causing few problems however in cases where their size begins to interfere with vital body functions.

Clinical Signs of Melanoma


Clinical signs depend on the location and size of the tumor. 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. Since over 80% of melanoma lesions will ultimately develop some degree of malignancy, early recognition and treatment are key for managing the disease.

Management and Treatment of Equine Melanoma


Treatment options include surgical removal, cimetidine, acupuncture, Chinese herbs, and a recently introduced vaccine. Large tumors can obstruct the rectum or prepuce, inhibit food intake, and impinge upon the upper airway. Surgical excision of the mass is usually locally curative, but is controversial for large or confluent tumors. In one study, 50% of horses who had tumors larger then 4 cm surgically removed, had continued or new growth of distant melanocytic tumors.

Symptoms

Pigmented raised nodules

Diagnosis

  • History
  • Clinical signs
  • Physical exam
  • Biopsy

While waiting for your veterinarian

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

Support

Therapies

TherapiesDetails
OnceptĀ® vaccineA DNA-based vaccine developed to treat melanoma in dogs, has also proven to be an effective treatment of melanoma in horses. The vaccine works by stimulating the body to produce an immune response to a protein found in melanoma cells (tyrosinase). The drug is licensed for use in dogs in the USA, and only available at select veterinary clinics. Treatment with the vaccine involves an initial assessment followed by administration of the vaccination at two week intervals for four treatments and then six-monthly boosters. Preliminary results from use of the vaccine suggest that response to the vaccine is positive in some cases but unpredictable; some horses showed cessation of melanoma growth or even tumor shrinkage, however not all horses responded to treatment.
CimetidineDaily oral supplement, at a dose of 2.5 mg/kg body weight, twice a day. It 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 excisionThe mainstay 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.
Chinese herbal medicineNei Xiao Luo Li San, Nei Xiao Wan, and Si Jun Zi Tang
Frankincense oilDaily injections of medicinal grade, sterile frankincense oil directly into the tumors, plus application of oil on topical tumorsJ Robertson, DVM

Prevention

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

Arabian iconLipizzaner iconPercheron icon

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