Small, wart-like skin changes or larger nodular growths – sarcoids are the most common skin tumors in horses. Even though they are not malignant in the classic sense, they can cause significant problems and tend to recur. Many horse owners are unsure: wait and see or treat? Which therapy is the right one? In this guide, you will learn how to recognize different types of sarcoids, why early action is important, and which modern treatment methods really help.

What is a sarcoid and how does it develop?

Equine sarcoid is a skin tumor that is often caused by infection with bovine papillomavirus (BPV). Although the tumors grow locally and do not metastasize (spread), they can be very persistent and often recur after treatment.

How does a horse become infected?

The exact transmission is not fully understood, but the following routes are suspected:

• Transmission by insects, especially flies and horseflies, which carry the virus from horse to horse
• Direct contact between horses is possible, but it is not the main mode of transmission.
• Contact with contaminated objects (cleaning equipment, saddlery) is also a possible route of transmission.
• Cattle can serve as a virus reservoir – horses grazing in pastures with cattle contact may be at greater risk.

Why doesn't every horse get sarcoids?

There is a genetic predisposition—some horse breeds and bloodlines are more susceptible. Quarter horses, Appaloosas, Arabians, and warmbloods are particularly commonly affected. The immune system plays a central role—a weakened immune system promotes development. Young horses aged 2–6 years are more commonly affected, but sarcoids can occur at any age.

Where do sarcoids occur in horses?

Preferred sites are areas where the skin is thin or areas that are subject to a lot of mechanical irritation. The most commonly affected areas are:

• Head area, especially around the eyes and ears 
• Abdomen and groin area, inner thighs 
• Elbow and belt position

Have you noticed skin changes on your horse? The specialists at Altano clinics can reliably diagnose sarcoids and recommend the best treatment. Find a clinic near you now.

Recognizing the different types of sarcoids

There are various forms of sarcoids, so it is not always easy to recognize a sarcoid as such. The correct diagnosis can only be made by pathohistological examination after removal of the tumor. The different types of sarcoids can also occur together in one patient; there is a mixed form, and they can develop into other forms. Sarcoids sometimes do not grow for a long time, but often become larger suddenly when manipulated or irritated. There are no harmless sarcoids.

Type 1: Occult (hidden) sarcoid

Appearance:

• Round, flat, hairless, or slightly flaky areas
• Often with fine creasing or "cigarette paper" texture
• Inconspicuous, easily confused with fungal infections or chafing

Characteristics:

• early stage
• Can remain stable for months or transform into other forms

Type 2: Verrucous (wart-like) sarcoid

Appearance:

• Wart-like, gray-brown, dry
• Rough, crusty surface
• Sometimes with stalked, cauliflower-like areas

Characteristics:

• Slow growth
• Mechanical irritation (rubbing, cleaning) can activate it, causing it to develop into a fibroblastic sarcoid.

Type 3: Nodular sarcoid

Appearance:

• Firm, round lumps under the skin
• Smooth, taut surface
• In some cases covered by normal skin
• Size: hazelnut to fist-sized

Characteristics:

• Often occurs in the groin, on the hose or udder, and on the inner thighs.
• When the capsule is opened, the risk of fibroblastic degeneration increases.

Type 4: Fibroblastic sarcoid

Appearance:

• Moist, bleeding, fleshy, "raw meat" character
• Often with ulcerations, may look like wild flesh of a wound
• May develop heavy exudation or foul odor

Characteristics:

• Growing very rapidly
• sensitive to external stimuli and trauma
• Treatment more difficult, high recurrence rate

Type 5: Mixed sarcoid

Appearance:

• Combination of verrucous, occult, nodular, and/or fibroblastic components
• Often large or extensive herds

Characteristics:

• Behavior difficult to predict
• Therapy must be individually tailored to the dominant components.

Type 6: Malignant sarcoid ( rare but highly aggressive)

Appearance:

• Strangular, inflammatory, ulcerating lesions
• Along lymphatic vessels or surgical scars

Characteristics:

• Pronounced invasive growth
• Can disfigure large areas
• Forecast significantly worse

The specialists at Altano clinics can reliably diagnose sarcoids and recommend the best treatment. If necessary, look for a clinic near you!

Why "wait and see" is not a good strategy

Many horse owners are tempted to simply observe small sarcoids at first. However, this can be dangerous for several reasons:

Growth: Sarcoids usually grow continuously, even if slowly. Even sarcoids that remain unchanged for a long time usually start to grow larger at some point. The larger they become, the more difficult they are to treat.

Transformation: Harmless-looking occult or verrucous sarcoids can develop into aggressive fibroblastic forms—especially after injury or irritation.

Location: Sarcoids in critical areas (eyelids, ears, genital area) can cause functional disorders. A small sarcoid on the eyelid can still be treated effectively—a large one cannot.

Treatment success: Small sarcoids treated early have a much better prognosis than large, advanced ones. A sarcoid that can be removed early and in its entirety has a lower risk of recurrence.

As a general rule, a horse with sarcoids has skin cancer, which should be treated early and consistently. However, there are some exceptions: In very old horses and in cases of small, stable sarcoids in non-critical areas, close observation may be acceptable—but only after consulting a veterinarian! Even in these cases, regular veterinary checkups are important! If the sarcoids grow in size or change in appearance, they should be treated immediately.

Diagnosis: How the veterinarian diagnoses a sarcoid

A reliable diagnosis is important, as not every skin lesion is a sarcoid: your veterinarian will perform a clinical examination to assess the size, shape, location, consistency, and type of the skin lesion. They will also check for other sarcoids on the rest of the body. It is important to keep detailed records with photos for objective progress monitoring. 

A sarcoid cannot be diagnosed solely on the basis of clinical examination, but its appearance and location are often sufficient to make a tentative diagnosis. For a definitive diagnosis, a small tissue sample, known as a fine needle biopsy, can be taken and examined histologically in the laboratory. In most cases, however, direct surgical removal followed by laboratory examination is preferable, as the skin lesion often needs to be removed regardless of the exact cause.

Differential diagnoses for equine sarcoids include other skin tumors such as melanomas (especially in gray horses) or squamous cell carcinomas (particularly common on the penis). Direct treatment is also necessary for these changes. Excessive granulation tissue after an injury (also known as "wild flesh") can resemble a sarcoid in appearance, but can usually be differentiated based on the patient's history. 

Modern treatment options: What really helps

There are numerous treatment options available for sarcoids today. No method guarantees 100% success, but the chances of recovery have improved significantly in recent years. Depending on the location, size, and type of sarcoid, your veterinarian will recommend the most appropriate option for your pet's specific case.

1. Surgical removal

If the size and location of the sarcoid allow it, complete surgical removal of the tumor is always the treatment of choice. Smaller, clearly defined sarcoids in areas with a lot of healthy tissue can often be successfully removed surgically. The chances are good that they will not recur afterwards. However, it is important that at least two centimeters of healthy tissue around the tumor is also removed. If it is not possible to remove the tumor in healthy tissue, surgery can be combined with other treatment options.

2. Removal by laser surgery

In this procedure, the tumor is also removed surgically, but instead of a scalpel, a laser is used, which simultaneously cauterizes blood vessels and sterilizes the incision sites. CO2 lasers or Nd:YAG lasers can remove sarcoids precisely and cause less damage to the surrounding tissue. Laser surgery is particularly suitable for sarcoids in sensitive areas (eyelids, genital area). Removal by laser can be combined with other treatment options, just like removal by scalpel, to reduce the risk of recurrence.

3. Intratumoral electrochemotherapy

This treatment combines chemotherapy and electrical impulses. A chemotherapeutic agent (e.g., cisplatin) is injected directly into the sarcoid. The electrical impulses open the cell membranes of the tumor cells, allowing the chemotherapeutic agent to penetrate more effectively. This modern therapy method is suitable for many locations (including the eyelids) and is highly effective. The treatment must be carried out by an experienced veterinarian, and several sessions are usually necessary. Special protective measures are required when handling chemotherapy drugs.

4. Combination therapy

Laser surgical removal of the sarcoid followed by electrochemotherapy of the remaining wound edges is particularly effective. According to current scientific knowledge, this is the treatment with the highest success rate. This combination is the treatment of choice, especially when sarcoids cannot be completely removed surgically due to their size or location.

5. BCG immunotherapy (tuberculin vaccine)

BCG is a tuberculosis vaccine that is injected into the sarcoid and triggers a strong immune response. Several injections can be given at 2-week intervals. This method is a particularly good option for periocular sarcoids.

6. Topical therapy with ointments and creams

Topical treatment alone should only be used for sarcoids if surgical excision is not an option. After removal with a scalpel or laser, the use of ointments or creams may be indicated to minimize the risk of recurrence. There are various options available for this:

• 5-fluorouracil ointment: Chemotherapy drug that blocks cell division and causes an inflammatory reaction
• AW4 solution (Liverpool Cream, 5-fluorouracil + heavy metal salts): most commonly used topical therapy, cream is applied by the veterinarian at intervals, causes a strong inflammatory reaction
• Aciclovir cream: Aciclovir is an antiviral medication that stimulates the immune system and has few side effects. 
• Imiquimod (Aldara cream): strong stimulation of the immune system, causes local inflammatory reaction

7. Cryotherapy (freezing)

Sarcoids are frozen with liquid nitrogen, destroying the infected cells. Several treatments are usually necessary, and severe swelling may occur after treatment. This method is particularly suitable for small, superficial sarcoids, but in most cases these can also be removed surgically. 

8. Radiation therapy (brachytherapy)

This involves inserting radioactive implants directly into the sarcoid. This method is particularly effective for large sarcoids. One disadvantage of this method is that it is very expensive and is only offered in specialized clinics. In addition, the horse must be isolated during treatment for radiation protection reasons. Only a few clinics in Europe have the logistical capabilities to offer this therapy.

Does your horse have a sarcoid and you are unsure about the best treatment? The experts at Altano Group will advise you individually. Get in touch now.

Avoiding recurrence: How to reduce the risk of relapse

Sarcoids are what are known as semi-malignant tumors, which means they tend to recur but do not metastasize to other parts of the body. These measures help to reduce the risk of recurrence:

During treatment:

• Consistent implementation of therapy – do not stop prematurely!
• Avoid any irritation of the treated area. 
• Insect protection – flies can interfere with healing 
• Monitor healing closely

After successful treatment:

• Regular check-ups of the treated area by the veterinarian 
• Photographic documentation for comparison purposes 
• Act immediately at the first signs of a recurrence! 
• Strengthening the immune system through optimal feeding and husbandry

Long term:

• Regularly check your entire body for new sarcoids.
• Insect protection throughout the grazing season 
• Pay particular attention to good wound healing in the case of new injuries – wild flesh can develop into a fibroblastic sarcoid.

Do you need support with follow-up care and recurrence prevention? The veterinarians at the Altano Group will accompany you throughout the entire treatment process. Make an appointment.

What you should definitely not do

Cutting them yourself or trying "home remedies": This can cause occult or verrucous sarcoids to become aggressive! Alternative methods such as the use of thuja or tea tree oil often lead to a severe deterioration of the condition due to local irritation.

"Wait and see": Small sarcoids are much easier to treat than large ones. Early treatment pays off! Unfortunately, it is unlikely that a sarcoid will shrink or disappear on its own.

Stop treatment when things look better: Many therapies take weeks or months. Stopping too early can lead to recurrence.

Prevention: Can sarcoids be prevented?

There is currently no scientifically proven, truly effective prophylaxis against sarcoids in horses. However, there are important measures for minimizing risk that are considered useful according to current veterinary knowledge. 

1. Avoid skin injuries, as bovine papillomaviruses enter the skin through microscopic skin lesions. 
2. Insect protection, especially during grazing season 
3. Consistently treat wounds hygienically (cleaning and disinfection)
4. Reduce contact with sick horses (no shared grooming equipment)
5. Keeping the immune system stable – no direct protection, but better tumor defense

In addition to these measures, regular monitoring and early intervention are most important. The earlier a sarcoid is detected and treated, the greater the chances of successful therapy.

Conclusion: Act early, treat correctly, follow up consistently

Sarcoids in horses are the most common skin tumors and should neither be ignored nor taken lightly. 

Equine sarcoids are benign but locally very aggressive skin tumors that usually continue to grow and spread without treatment. It is important to note that sarcoids do not disappear on their own, can even worsen due to friction or improper manipulation, and often give rise to new lesions. Early veterinary diagnosis and appropriate, individually selected therapy significantly improve the chances of success and prevent small changes from becoming large, difficult-to-treat tumors.

Since every sarcoid reacts differently, there is no standard treatment, but there are many effective options—from medications and ointments to surgical procedures, laser therapy, and immunomodulation. It is crucial not to irritate the tumor, to work closely with your veterinarian, and to monitor changes regularly. 

With timely intervention and the right treatment, sarcoids can often be controlled effectively and the horse remains symptom-free in the long term.

For better readability, we predominantly use the generic masculine in our texts. It goes without saying that all personal designations refer equally to all genders. The abbreviated form of language is used solely to improve comprehensibility and is to be understood in an unbiased manner.