Sarcoids In Horses

Sarcoids In Horses: What You Should Know

Sarcoids are the most common skin tumour found in horses, which means that it’s important for horse owners and riders to monitor their horses for any signs of the condition. However, there are multiple sarcoid types to look out for, with each one having its unique characteristics.

In this article, we’re hoping to shed some light on these growths and help you to better understand what they are and what they look like. We’ll also explore possible causes and treatments for the condition so that you’re well-prepared to care for your horse.

What are Sarcoids in Horses?

Sarcoids are a common type of skin tumour that commonly affects horses. In fact, this skin cancer actually accounts for around 40% of all equine cancers. These tumour cells are locally invasive, and they are known as fibrosarcomas, which means that they grow and spread within the skin but don’t metastasize to other organs.

These tumours can manifest in different ways, such as flat or warty areas of the skin, as well as nodular skin lumps. This skin cancer is usually persistent and progressive, and while it can occasionally disappear spontaneously in your horses, this is extremely rare.

Skin sarcoids can occur in almost any area of the horse’s body, but are most commonly found in the groin, around the armpits and chest area, head, and inner thighs. They may also appear near old scars, particularly on the legs. This is because these areas are more prone to fly bites, which can potentially contribute to the growth of sarcoids.

Sarcoids can affect horses of all ages, breeds, and sexes. However, it has been suggested that geldings, which are castrated males, are more at risk to develop sarcoids than mares.

Types of Sarcoids

There are several types of sarcoid that can affect a horse. Each type has a distinct appearance and certain characteristics that make it easy to discern between them.

As a horse owner, it may be helpful to know what to look for, and how to discern between marks or scars on normal skin and sarcoids. Since it’s the most common skin tumour found in horses, you’ll want to be prepared. However, it’s important to remember that you should always consult an equine veterinarian for a diagnosis and treatment options going forward.

There are six main types of sarcoid, which include:

Occult sarcoids

Occult Sarcoid

An occult sarcoid is the earliest and least aggressive form of sarcoid. They may be tricky to identify, especially if your horse has a thicker coat. Because of their appearance, they are also sometimes mistaken for ringworm or rub marks from tack.

These sarcoids commonly appear as circular areas of grey skin that have different hair quality or where there is a lot of hair loss. There may also be some thickening to the skin, and it may have a scaly surface. If you feel the area, you can typically feel small nodules or skin lumps under the area, which is the easiest way to discern between sarcoids and other conditions.

Verrucous sarcoids

Verrucous sarcoids are slow-growing lesions that may resemble warts and typically have a flat or thin appearance with rough or scaly skin. Like an occult sarcoid, they can also be grey in colour and can resemble scars. However, the appearance of warty skin is usually a tell-tale sign that the underlying cause is sarcoids.

When verrucous sarcoids start out, they may have an ‘occult halo’, which describes an area of hair loss or thinning around the sarcoid. Within the sarcoid, small solid nodules can sometimes be felt under the skin. As they develop, the skin around the tumour cells becomes more scaly and flaky. It can sometimes look like dandruff and will fall off of your horse’s skin if you rub it.

In more severe cases of this cancer, some localized ulcers can develop. They can look red and fleshy and are normally open or exposed.

Nodular sarcoids

A nodular sarcoid is easy to see and identify on your horse’s skin. Of course, given the name of this tumour, the most common sign is hard nodules under the skin. These nodules can differ in size, and can even look like a bunch of grapes when there are multiple nodules present.

There are two types of these sarcoids, including:

Type A

Type A1 sarcoids can be moved freely over the horse’s skin’s surface, and don’t generally have any attachments to any of the tissues around it. Type A2 sarcoids, on the other hand, have deep attachments to the underlying tissues. If a horse has Type A2 sarcoids, it will need surgery or litigation to remove them and, unfortunately, recurrence is common.

Type B

Type B sarcoids are more firmly attached to the overlying skin and can sometimes infiltrate the surrounding tissues. Much like Type A, Type B1 sarcoids don’t have attachments to underlying tissues, but it is attached to the overlying skin. Type B2 sarcoids are a more severe form of the condition, and the tumour usually penetrates the skin and tissues.

Fibroblastic sarcoids

Fibroblastic sarcoids are aggressive tumour cells that grow quickly and tend to invade the tissues under the skin. They can sometimes appear in clusters, but, because of their rapid growth, they are prone to bleeding or causing ulcers if they are agitated.

The open flesh can sometimes attract flies in the summer, which can lead to maggot infestations in the wound. So it’s important to ensure that the wound is tended to regularly.

Like nodular tumours, fibroblastic sarcoids can be split into two main types:

Type 1

This type of sarcoid normally has a narrow stem where it attaches to the horse’s body. Depending on the presence of the sarcoid, it can be divided further into two subgroups.

  • Type 1a: These don’t have any root extension beyond the stem.
  • Type 1b: These sarcoids also have a stem, but it has roots that extend into the body. Usually, the treatment plan for horses affected by Type 1b fibroblastic sarcoids depends on whether it has extensive roots or not.

Type 2

This type is also known as sessile or rooted sarcoids, but they don’t have a stem. These tumours are an indication of a more severe case of the condition, which makes treatment for Type 2 sarcoids more difficult.

The roots of these sarcoids are thick and can penetrate deeply into the skin. This makes them more susceptible to bleeding and infection, which means you’ll need to keep a close eye on the wounds.

Mixed sarcoids

Aptly named, mixed sarcoids mean that there are multiple sarcoid types present. They can also appear over different parts of your horse’s body, forming clusters or colonies of tumours. Usually, this type of sarcoid is created by at least two other types of sarcoid, and the different types can exhibit different characteristics and behaviours.

When a mixed sarcoid is diagnosed, the vet will want to identify the main type to determine the most effective treatment. However, this can be tricky when there is a combination of more than two sarcoid types.

Malignant sarcoids

Malignant or malevolent sarcoids are the most aggressive type and have a poor prognosis. Luckily, instances of this type of sarcoid are rare and don’t affect as many horses as any of the other types.

It’s important to remember that while malignant tumours describe those that spread to other parts of the human body, it works differently in horses. Instead, it spreads locally via lymph vessels. This is what causes the formation of lines of sarcoids in the skin that originate from the primary tumour site.

Horses that are affected by malignant sarcoids usually have multiple sarcoids in different areas of their bodies. However, single malignant sarcoids can develop on their own – particularly around the elbows, medial thighs, and on the sides of the face.

Causes of Sarcoids

The main cause of sarcoids in horses is an infection with the Bovine Papilloma Virus (BPV). Still, not every horse that has been infected with Bovine Papilloma Virus will develop sarcoids. Instead, it usually affects genetically susceptible horses who are infected.

When a horse is infected with BPV, it’s likely that the horse will carry the virus for the duration of its life. And, if the horse is genetically susceptible, it’s not uncommon for it to develop sarcoids again in the future.

Unfortunately, the exact cause of the development of sarcoids is unknown. There has been some evidence to suggest that insects like flies can cause the condition, but this hasn’t been confirmed.

While BPV is only one potential factor that can lead to sarcoids, the same BPV cells that are found in sarcoids are also present in normal skin. The only difference is the amount of the virus that is found in sarcoids is much higher.

How To Treat Sarcoids

The treatment options for sarcoids differ depending on the size, location, and extent of the tumours that the horse is presenting. It’s important to remember that there isn’t a universal treatment for sarcoids. So, if your horse is suffering from this condition, it may receive any one of the available treatments.

Before your horse receives any treatment, your local equine vet will need to assess your horse and determine the correct treatment plan based on what’s best for your beloved riding companion.

Medical treatments

There are several medications and medical treatments that can help to treat sarcoids or reduce their impact on your horse’s quality of life. For example, the BCG vaccine (which is used to prevent tuberculosis) can sometimes be injected into the infected skin cells to stimulate the immune system, while chemotherapy drugs like cisplatin and Mitomycin C interfere with DNA copying in the tumour cells.

There are also topical chemotherapy creams like AW4-LUDES, also known as Liverpool Cream, and certain ointments containing bloodroot plant extracts that can help to lessen the discomfort or shrink the tumours.

Surgical treatments

Some of the surgical options available for sarcoids include surgical excision, cryosurgery, laser surgery, and electrochemotherapy. However, surgical excision without any additional therapy has a high failure rate, and recurrence of the condition is common.

Cryosurgery involves freezing the tumour to destroy it, and laser surgery uses a laser to cut around the sarcoid. Both of these methods isolate the tumours to remove them, which also means there is a minimized risk of spreading the cancer cells when they are removed.

Electrochemotherapy is a highly effective treatment method. It involves injecting chemotherapy into the tumour before using high-voltage electric impulses to increase the effects of the drugs.


What is the prognosis for sarcoid in horses?

The prognosis for sarcoids in horses can change depending on the severity of the tumour, where the tumour is located, and the way that the horse responds to treatment. Sarcoids are unfortunately difficult to treat, and there is a high chance of recurrence – even after it has been successfully treated.

Are sarcoids in horses contagious?

Currently, the extent of sarcoids and their potential for spreading is still a topic of debate and research. Still, many of the cases are closely associated with Bovine Papilloma Virus (BPV), which may give some clue as to how (or if) they spread. It’s important to remember that not every horse with BPV will develop sarcoids, though, so it doesn’t mean that a spread of BPV will necessarily lead to a spread of sarcoids.

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