My horse has melanoma, now what?!
About 80% of gray horses over the age of 15 have melanoma, but in most cases, the tumors first appear much younger. This is the result of the formation of melanoma being linked to the graying gene in horses (STX17).
That means, you're not alone! This is a common struggle, especially in breeds that have a high gray horse population like Quarter Horses, Arabians, Andalusians, and Warmbloods just to name a few.
So, how do you know its melanoma?
Melanoma usually starts as small pinpoint raised areas that are darkly pigmented. Typical locations for the skin bumps are under the tail, around the anal sphincter and vulva, on the sheath or penis, and at the commissures of the lips. However, they can form anywhere and may not be just on the skin, but also under the skin in haired regions. Tumors can also occur on or at the base of the ear, behind the jaw line where the parotid salivary gland lives, on the eyelids, and even in the eye itself (ocular melanoma).
Tumors can be biopsied to confirm the diagnosis, however, if they are black in color, on a gray horse, and in a typical location, the diagnosis of melanoma is assumed.
Melanoma can occur in non-gray horses, but it is rare. In these cases, it is not tied to a color gene and is often more aggressive.
What can you do to treat it?
You may have heard some veterinarians say, “leave it alone.” Please don't do this!
Your veterinarian is great, me being one, but sometimes they don't know the latest cancer research and I don't fault them! It's difficult to be up to date on everything and not everyone is a cancer expert.
Here are my recommendations:
Treat them early and keep on top of it. Small melanomas should be surgically removed or laser ablated.
Consider a melanoma vaccine.
There is the commercially available Oncept vaccine, originally manufactured for dogs, that has now been used in horses for years. The down side: It requires a specially administration device, it is sometimes in low supply, and it costs about $600 per dose. They initially need 4 doses, two weeks apart, then a dose every 3-6 months there after.
There is also an option for an autologous vaccine. This is a vaccine made form your horse's own tumor tissue. It can be sent to a company that processes the tissue and makes it safe for injection. One of the more common companies is called Torigen. It costs about $1500 for them to make it. That does not include your veterinarian’s fee to remove the mass and send it out. They make a series of three vaccines that are shipped to your vet and administer subcutaneously once a week for three weeks.
Consider preventatives
Melanoma is genetic in gray horses, there is no way around it. However, there are steps we can do to help. Consider adding herbs to the diet that decrease inflammation and have been shown via research to target tumor cells.
Some veterinarians also recommend Cimetidine. This is not wrong, but there is mixed evidence that is works and the horse needs to be on it for their entire life. This means bloodwork should be performed every 6-12 months to ensure there are no adverse effects.
Commonly asked questions:
Can chemotherapy be used to treat melanoma?
Yes. When chemotherapy is used in horses, it is most commonly used locally. This means, the chemotherapy agent (most commonly cisplatin) is injected into the tumor. Chemotherapy works by invading rapidly dividing cells (tumor cells), binding to DNA and disrupting cellular mechanism leading to cell death.
Sounds great! Why doesn't this seem to work well for equine melanoma?
Melanotic tumors are very dense, making it hard to inject the chemotherapy agent. Secondly, melanoma cells seem to be some what resistant to local chemotherapy. It is believed to be due to the fact that they are slower growing and the amount of time the chemotherapy agent is present is in the tissue is not enough time to kill a large portion of cells. We can increase the potency by adding an electric current (electrochemotherapy), but this has to be done under general anesthesia and unfortunately still doesn't provide significant results. At best, this is used as a maintenance treatment to keep tumors at bay that are beyond surgical intervention.
Will the melanoma get bigger if my vet doesn't remove all of it? Will it “blow up?”
No, melanoma does not behave that way. This is a common misconception that comes from treating sarcoid. It is best to remove melanoma, or “debulk,” which means remove a large portion. I have never seen a melanoma get “angry” like a sarcoid, nor have any of my specialist colleagues.
Are there topical options, like those available for sarcoid and squamous cell carcinoma?
There are no prescription options available for equine melanoma. Crazy, right?!
In fact, there are no commercially available options for topical treatment of equine melanoma at all.
Some compounds have been tested with modest results, one being Betulinic acid. The research was done using very small tumors and some reduction in tumor size was seen over a 3-month period. The tumors were not gone, but some were smaller after twice daily application for 90 days. However, a new study published this year showed no difference in tumor size after daily application for 30 days.
Based on human research and veterinarian designed, we developed our own product, “Gray-Out.”
Gray-Out contains Boswellic acid from Frankincense, similar to the studied Betulinic acid. It also has Turmeric, Green tea Grapeseed oil, Nicotinamide, Hyaluronic Acid, Bakuchiol, Centella Asiatic, and Tranexamic Acid (TXA). These ingredients are skin nourishing, anti-inflammatory, anti-oxidant, and have published research regarding melanoma. We have also paired this topical product with our oral supplement Lifespan (Boswellia, Turmeric, Vitamin C, Black Pepper, and Flaxseed) as a dynamic duo for supporting horses with skin tumors.
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