Equine Melanoma

Equine Melanoma

What is Melanoma?

Classifications

Causes/Management

Treatments

Final Thoughts

Melanoma in Horses - Clinical Signs

What is Melanoma?

• Melanoma is a form of skin cancer that can be fatal to humans because the cancer cells often metastasize to multiple organs in the body.

• Melanoma is a result of abnormal proliferation and accumulation of melanocytes (pigmented cell within the dermis).

• In horses melanomas appear as round black nodules and are not painful
• Prevalence of melanoma in gray horses over 15 years is estimated at 80%
• Most common sites for melanotic tumors:
• Parotid gland (base of the ears)
• Around the eyes
• Around the mouth
• Around the neck
• Under the tail near the base
• On the prepuce

Common Sites for Melanotic Tumors

Equine Melanoma in Gray Horses

Classifications of Melanomas in Horses

• Benign Dermal Melanoma
• Develop in older gray horses
• Rarely metastasize

• Malignant Dermal Melanomatosis
• Multiple and interspersed
• high likelihood of metastasizing in gray horses older than 15 years

• Melanocytic Nevi
• Younger horses irrespective of color
• superficial, benign and discrete lesions

• Anaplastic Malignant Melanoma
• Rare and tend to occur in non-gray older horses
• Tend towards organ metastasis

Multiple Melanoma

• Multiple melanomas are common in gray horses
• Can form near vital organs
• Lumps near a horses rectum can lead to problems urinating, defecating, and breeding
• Can cause discomfort if the lumps are found in the saddle or bridal area

Treatments for Melanoma

• Surgical Excision
• Not possible with large or multiple confluent masses

• Cryonecrosis
• Freezing with liquid nitrogen
• Used as a primary entity or as an adjunct to surgical excision

Treatments for Melanoma

• Chemotherapy
• Injection of cisplatin emulsion, or placement of cisplatin-containing biodegradable beads
• Cisplatin has poor effectiveness against melanomas in dogs and people, but has been used with success in at least one clinical trial in horses

• Cimetidine
• Anti-ulcer medication
• Some good results have been obtained, but continued, long-term use can cause resistance and reduce the tumor-shrinking effects

• Frankincense Oil
• Applied topically, frankincense oil has been shown to reduce tumor size
• Testing continues on this promising therapy

• Gene Therapy
• As melanomas are thought to be the result of mutations, there is research on identifying the cause of these mutations
• Gene therapy may enable the manipulation genetic signals to prevent cells from becoming cancerous, or turn off cancer-like functions once they begin

Treatments for Melanoma

• Thermal Therapy
• Thermofield microwave diathermy system developed by Parmenides, Inc.
• A type of cancer treatment in which body tissue is exposed to high temperatures
• At a high enough temperature (43°C - 46°C) heat kills cells in solid tumors, without damaging normal tissues
• Heat can also increase the efficacy of adjuvant radiation therapy and chemotherapy

• A melanoma vaccine being tested
• DNA vaccine that ‘target’ cancer cells
• Melanocytic tumors have a high level of tyrosinase
• DNA vaccine helps immune system identify and kill cells with elevated tyrosine levels

Causes of Melanoma

• Likely a number of mutations linked to coat color
• Horses with the gray gene
• Excess melanin is not evenly distributed and forms into clumps that become melanomas

• Some scientists believe sun exposure plays a role however not all sites are exposed to sunlight

Management of Melanoma

• In most cases melanoma will cause no problems

• Watch out for these signs:
• Spreading of the melanoma
• Difficulty defecating or urinating
• Problems with vision or hearing
• Listlessness or change in personality