Sarcoids are a type of skin tumour; they are the most common skin tumour in horses. They are tumours of fibrous connective tissue (fibrosarcomas). Although they are a form of skin cancer, they only spread locally in the skin, and they do not spread inside the horse (they do not metastasise internally). They affect horses of all breeds, colours, age and sex (although there is a suggestion that geldings are more commonly affected than mares).

Sarcoids are caused by infection with bovine papilloma virus (BPV). Not every horse or donkey infected with this virus will develop sarcoids – animals with a specific genetic (inherited) susceptibility will develop sarcoids when they are infected with BPV, whereas horses without this genetic susceptibility will not.

Once a horse is infected with BPV, it is likely that this remains in the horse for life (once a sarcoid horse, always a sarcoid horse!). As the genetic susceptibility also remains, horses that have been treated for sarcoids often get them again. BPV in horses behaves in a similar way to papilloma virus in people (which can cause cervical cancer in women) – the virus becomes incorporated into the DNA of infected skin cells and can cause a transformation of those cells into tumour cells.

It is possible that flies may spread the BPV virus from horse to horse (or from cattle to horses), however, this has never been proven.

Some people believe that sarcoids have spread from horse to horse in close proximity in the same yard, but again, this has never been proven and currently there is no strong evidence to suggest that horses affected by sarcoids are a threat to others.

Key points:

• Sarcoids are persistent and progressive skin tumours
• Genetically susceptible horses develop sarcoids as a result of exposure to bovine papilloma virus (BPV)
• Sarcoids commonly appear on the head, face, chest, groin but can develop anywhere on the skin
• Sarcoids are a form of cancer and are usually locally invasive but do not spread to other organs
• There are different types of sarcoids: because they behave differently and respond to different treatments, they need careful veterinary assessment before deciding on treatment
• An individual horse may have a mixture of different types of sarcoids

There are various treatments and the correct treatment must be chosen for each sarcoid because inappropriate treatment can make sarcoids more aggressive and may make the situation worse

There are 6 main types of sarcoid, although many horses have a combination of different types. These different forms of sarcoid behave differently (some types are faster growing and more aggressive than others), however, it should be recognised that a sarcoid can change its behavour from a benign, inactive type, to a faster-growing, more aggressive type. This commonly occurs when an inappropriate / ineffective treatment is tried and the sarcoid grows back more agressively than before.

Biopsies can also make sarcoids more aggressive and they are generally not recommended unless they are carried out in combination with treatment.

The different types of sarcoids include the following
 

OCCULT

These are the earliest and least aggressive form of sarcoid. They can be difficult to spot, especially with a thick winter coat. They can sometimes be confused with ringworm or even rub marks from tack. They can remain static for years, or they may change to other form, especially if they become traumatised.

They have the appearance of a roughly circular area of altered hair quality / colour (or maybe hairless) with mild thickening / scaliness of the skin. There may be numerous tiny nodules / lumps in the affect area of skin. Occult sarcoids are commonly seen on the nose and the side of the face, the armpit and on the inside of the thigh or groin.

VERRUCOSE:

These sarcoids are slow growing, wart-like lesions. They are usually flay or thin and have a rough, scaly surface; they are often grey in colour. They may sometimes be confused with scars. Verrucose sarcoids also tend to be slow-growing and benign.

NODULAR:

These are well-demarcated lumps, which may be covered by normal skin or may be ulcerated. They are usually spherical, but may have a wide, flat base of narrow stem-like base. They may be single or occur in group and are variable in size.

Nodular sarcoids are variable in their behaviour – most tend to get bigger with time, but that timescale maybe fast or slow. They can also change their behaviour and some will change from nodular to fibroblastic.

FIBROBLASTIC:

These sarcoids are aggressive tumours that tend to rapidly grow and are locally invasive, sometimes invading down into the tissues underneath the skin. They can occur in clusters of tumours of variable size and shape and have an irregular appearance. Because they grow rapidly, they are usually ulcerated and bleed easily if traumatised.

They can be confused with proud flesh (exuberant granulation tissue). In warm weather they often attract flies and can become infested with maggots.

MIXED SARCOIDS:

These are combinations of the above types of sarcoids. It is common for there to be multiple sarcoid types present at different sites around the horse.

MALIGNANT / MALEVOLENT SARCOIDS:

This is the most aggressive type of sarcoid. Fortunately, they are uncommon.

The name ‘malignant’ is a bit misleading – sarcoids do not behave like other malignant cancers in spreading throughout the body. These types spread locally via lymph vessels, producing lines of sarcoids (often ulcerated, nodular types) in the skin, spreading from the original tumour site. There is no effective treatment for this type of sarcoid.

There is no single treatment that will work for all sarcoids. The different behaviour of different types of sarcoids means that different treatments are required for different circumstances. Some of the factors that need considering when deciding what form of treatment is appropriate for a particular horse include:

• The number and type of sarcoids
• Location of the tumours
• Temperament of the horse
• Treatment costs

In addition to differences in the behaviour of the different types of sarcoid, the location on the body also affects the treatment choice. Sarcoids in certain areas, such as in the eyelids, can be particularly difficult to treat and surgical treatments may not be possible because of the subsequent deformity of the eyelid.

The internet is full of ‘home-cures’, including such things as toothpaste, turmeric, castor oil, herbal creams, apple cider vinegar, duct tape etc. There is absolutely no evidence that these ‘treatments’ work and there is a definite risk that they could actually aggravate sarcoids and stimulate them to become more aggressive. There is no ‘magic cure’.

The most important recommendation for treatment of sarcoids is to treat them when they are small and manageable. The bigger and more aggressive they become, the more difficult treatment becomes. Get advice from your vet as soon as you notice a sarcoid.

TREATMENTS

As sarcoids are extremely unpredictable, there are a vast variety of treatment options. Please consult the veterinary team at BELL EQUINE on 01622 813700 before proceeding with any treatment option, especially as inappropriate treatment can cause sarcoids to become worse.

BENIGN NEGLECT:
Occasionally your vet will advise you to just monitor a small sarcoid that has recently developed. Some sarcoids may stay very small without further development for years, so occasionally benignneglect is the treatment of choice. However, if the sarcoid starts to grow, then treatment is likely to be required.

MEDICAL TREATMENTS:
 

Bacillus Camette Guerin (BCG) vaccine:
Also used to prevent tuberculosis, this acts as an immune stimulant that can be injected into the tumour. It is especially useful for treating sarcoids in the eyelids. There is a risk of serious allergic reactions using this drug. Unfortunately, BCG is currently unavailable due to worldwide supply problems.

Chemotherapy Drugs:
Chemotherapy medications, such as cisplatin and Mitomycin C, can be injected into tumours. These act by interfering with DNA copying in tumour cells. Repeated injections over several weeks are usually required. The drugs cause inflammation and the sarcoids often become swollen and sore before they regress.

AW4-LUDES (‘Liverpool Cream’):
This is a topical chemotherapy cream that can be applied to the surface of sarcoids. It contains the chemotherapy drug 5-fluorouracil as well as a variety of heavy metals, cytotoxic chemicals and natural plant oils. The cytotoxic nature or the cream makes it dangerous to use; as such only veterinarians are permitted to apply the product. A typical treatment course involves four treatments over the course of one week.

Imiguimod (Aldara cream):
This is an immune response modifier with potent antiviral and antitumour activity that is used for treatment of skin cancer and genital warts in humans. A layer of cream is applied over the sarcoid initially three times weekly. It may take 2 – 4 months of treatment to see a decrease in tumour size and it is only likely to work on very small / thin tumours (such as occult and verrucose sarcoids).

Advantages of this treatment are that owners are able to apply the cream themselves (wearing gloves) and that it can be used over sensitive areas e.g. joints. However, horses often become sore when this treatment is used and therefore may become ‘difficult’ when applying the cream.

Blood Root Ointment:
This is a cream containing extracts of the blood root plant and various other natural chemicals. Treatment usually consists of daily or twice daily applications of the cream for 7 to 10 days. Owners are able to apply the cream and it is non-toxic. Again, this treatment can be useful in treating relatively small sarcoids, but doesn’t work in all cases.

SURGICAL TREATMENTS:

Surgical options include sharp surgical excision, cryosurgery (freezing) and laser surgery. Sharp surgical excision without additional therapy has poor success rates. Surgery followed by cryotherapy (freezing) improves success rate somewhat, but the majority of sarcoids still return following this approach.

Laser Surgery:
This surgical option is being increasingly used to treat sarcoids and is adaptable to treating many (but not all) types of sarcoids. The advantages of laser surgery over traditional sharp surgery includes the fact that the laser destroys (vaporises) the skin as it cuts; it therefore prevents sarcoids being spread around the wound, which can occur when a knife / scalpel is used. This significantly reduces the risk of sarcoid regrowth. In addition, there is less bleeding, less swelling and less pain with laser surgery.

In many cases, laser surgery can be undertaken in the standing, sedated horse (using local anaesthesia), thereby eliminating the risks associated with general anaesthesia. However, in some cases, general anaesthesia will be required because of the number, size and location of the sarcoids, as well as the temperament of the horse.

At BELL EQUINE we have a CO2 laser unit that is ideally suited to treating sarcoids. In most cases, the laser is used to excise (cut out) the sarcoid, including a margin of normal looking skin (which is important to reduce the recurrence rates); the wounds are usually left open and heal over the following few weeks (in most cases horses can be kept exercising lightly during this healing phase).

Electrochemotherapy:
This is a recently developed treatment that is available at BELL EQUINE. It involves the combined use of injecting a chemotherapeutic drug (usually cisplatin) into the sarcoid, followed by the application of high-voltage electric pulses (electroporation). This increases the drug concentration in the cells of the sarcoid by around 70 times, thereby increasing its effect. Due to the electric shock, the procedure must be performed under a brief (usually around 15 minutes) general anaesthesia. In some cases, we will advise combining ECT and laser surgery.

Radiotherapy:
Radiotherapy is often considered to be the ‘Gold Standard’ treatment for sarcoids because it has a high success rate and can be used to treat most types of sarcoid (except ‘malignant’ / malevolent sarcoids).

There are a number of different ways of performing radiotherapy. Unfortunately, this is a very specialised form of treatment that is only available at a small number of equine veterinary hospitals in the UK. Radiotherapy carries significant health and safety risks to people handling horses being treated in this way and it is extremely expensive, so is rarely used.