Equine melanoma. Detection and treatment.

Equine melanoma in perianal area

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Today we will discuss an important issue for equine health. And is that the health and welfare of horses is one of the priorities for Gustavo Mirabal Castro. That is why today we will talk about equine melanoma.

Equine melanoma is one of the diseases that is left untreated given its slow progress. However, with the appropriate treatments, it can be eliminated and / or delayed. That is why today we will give you information and some advice for its detection and treatment. Some treatments are not available in Spain, however, perhaps this type of information may arouse interest and begin to be considered.

We will learn more about equine melanoma thanks to the information in the article by J. Luis Mtnz Arquero published in “Dressage and horses”. Based on your article and some additional information we have developed this post. We hope you like it and we promote these initiatives.

What is equine melanoma?

They are tumors that usually appear as firm black masses, in the form of a potato, in areas without hair or with little body hair, as in the maslo.

When most people hear the term “melanoma,” they think of skin cancer caused by excessive sun exposure. In horses, however, melanomas are associated with the color of the layer, specifically the color of the layered layer.

Up to 80% percent of thrush horses have melanomas.

The gene responsible for thrush color is a dominant gene that causes progressive depigmentation of hair. These horses can be born of any color: black, brown, even paint, but colored hairs are replaced by white hairs as the horse ages.

The first signs of “gray hair” are found around the eyes or the nose in foals and can be seen on the day they are born. An aged gray horse could be called white, but true white horses have pink skin.

A thrush will have black skin and dark eyes.

Equine melanoma in perianal area

In which areas of the horse does equine melanoma commonly develop?

In most cases, equine melanomas appear alone in the perianal region. This is quite common in horses older than 6 years.

Equine melanoma can also appear in the parotid region, in the penis and in the periocular area.

On less common occasions, equine melanoma appears in animals less than 4 years old in the trunk and limb areas

Is equine melanoma malignant or benign?

Equine melanoma is a type of tumor, usually benign, that occurs more frequently in layered horses.

Despite this there are elements that help us differentiate malignant equine from benign melanomas.

When melanoma occurs multiplely in the same area of the horse, tumors are considered malignant.

A malignant melanoma can behave in different ways. The 3 behaviors that can have malignant equine melanomas can be:

Slow progressive growth without metastasis. This is the most difficult to identify and therefore runs the risk of letting it grow too much.
Slow progressive growth over years and subsequent rapid growth with metastasis. This change allows us to take action but requires horse monitoring and careful observation.
Malignant growth since its appearance. This is usually treated quickly because it arouses suspicion. These melanomas can be very aggressive and you have to take their treatment very seriously.

Occasionally, these melanomas can reach large size and if they are found in the perianal region, they can cause problems with defecation and urination

Detail of equine melanoma in perianal area

How does an equine melanoma develop?

Most equine melanomas have slow growth for years without metastases (it spreads throughout the body). This is why melanomas are generally considered benign in horses.

Some melanomas that have been static for years may suddenly grow and metastasize. A smaller percentage of melanomas will show rapid growth and metastasis from the beginning.

Melanomas found in horses that are not thrush are generally considered highly malignant. Metastasis can occur in regional lymph nodes near the original tumor or in body cavities or internal organs (lungs, liver or spleen).

Melanomas have also been found in muscles, spine, heart and guttural pockets. Many horses do not show clinical signs of internal metastasis, but lameness, cramping or neurological symptoms can occur.

Any dark mass in a thrush horse is presumed to be an equine melanoma and most are diagnosed only by appearance. A biopsy will confirm the diagnosis. It can indicate how malignant that particular tumor is, although it is not necessarily predictive of tumor behavior or metastasis.

Internal tumors can be found with ultrasound or rectal palpation.

While there is currently nothing we can do to prevent the development of melanoma, there are several treatment options available.

Traditionally, equine melanoma has been left alone due to its slow growth and lack of pain or clinical signs. On the other hand, early treatment can slow or stop the progression.

Equine melanoma

Veterinary solutions to equine melanoma

Small tumors are easily removed surgically. Depending on the location of the horse’s mass and temperament, they can often be removed with foot sedation instead of general anesthesia.

The use of surgical lasers have been very successful in removing an equine melanoma, even when the tumors are slightly larger. Complete excision will be curative for an individual tumor, but new tumors may arise later.

Below we can see a video of a laser surgery to treat equine melanoma

Very large tumors or those in difficult places may require extensive surgery and often cannot be completely removed.

Cimetidine that is an antihistamine has immunomodulatory effects. This has been reported to reduce the size and number of tumors. Long-term therapy (at least three months) is required and clinical efficacy has not been repeatable in all studies.

The intratumoral injection of chemotherapeutic agents, such as cisplatin, may be effective for small masses. However, there are still health and safety problems for the horse. There are even risks for the owner and the treating veterinarian when these medications are used.

The hope of the melanoma vaccine

Recently, a vaccine was developed for the treatment of melanoma in dogs. Early studies are proving promising for use in horses. This vaccine creates an immune response against melanoma cells, causing the body to fight against tumors. The vaccine is given four times at two week intervals. If the horse responds, the vaccine is given every six months.

At the moment I don’t know anyone in Spain who treats equine melanomas with this vaccine. For this reason I cannot tell you about my personal experience. All the data that I have collected here is easy and can be found in any veterinary book.

I am sure that in a few years treatments with the melanoma vaccine will be very common in Spain and other countries. And it is that the thrush color remains the most abundant in the Iberian equine horse.

From here we take care of spreading this technological advance so that it is adopted in a massive way. The treatment of equine melanoma through the vaccine will result in the welfare of the horse and its performance.

We hope that many veterinarians will be able to see in the future not only a business but also a way to fulfill their professional work better. Support us in our campaign.