1. Occult

   Appearance: Gray, flat and hairless areas of skin, often subtle in appearance especially in early development. The irregular skin is rough and may feel slightly thickened. Because of its circular or oval shape, occult sarcoids are often mistaken for ringworm.

   Traits: These sarcoids grow very slowly and may remain static for years. However, if accidentally traumatized, they can rapidly develop into one or more serious types of sarcoids, including fibroblastic.

   Found: On the nose, side of the head, neck, armpit and between the hind legs.

2. Verrucous

   Appearance: Can be gray, scabby, scaly or wart-like in appearance. They may contain small, solid nodules (growths of abnormal tissue) that appear singularly but often can merge into larger, multiple lesion groups. Verrucous sarcoids extend deeper than the occult type and have a more irregular outline and uneven surface that may resemble ringworm or scarring. The skin may crack easily and scaly flakes often can be rubbed off from the surface.

   Traits: Slow growing and the least aggressive sarcoid type, they are often non-painful on manipulation; however, interference may stimulate these lesions to change into a more aggressive form of sarcoid and potentially can develop into both fibroblastic and malevolent forms following inappropriate handling or treatment.

   Found: Around the head, groin, sheath and armpit body regions.

3. Nodular

   Appearance: Discrete, solid nodes with a spherical appearance. They may have a wide, flat base or a narrower stem-like base and can appear on their own but are often seen as well-outlined lumpy groups.

   Traits: Unlike other types, nodular sarcoids are covered and firmly attached by an overlying layer of normal skin. Even with the skin coverage, they have the potential to ulcerate and bleed. Agitating these lesions can result in rapid growth and possible transformation into a more drastic type, particularly the fibroblastic form. This type of sarcoid varies in size, some being more than 5 cm (2 inches) in diameter, with a medium growth rate subject to change over time.

   Found: Around the eyelids, armpits, inside thigh and groin areas.

4. Fibroblastic

   Appearance: Fleshy, irregular masses — often in clusters of tumors of variable size and shape that grow rapidly — typically having wet, bloody ulcerated surfaces. Fibroblastic sarcoids can begin as round or irregular, raised, firm lumps and are usually smooth and hairless at least over part of their surface; smaller ones are sometimes covered with normal skin.

   Traits: Can have a wide, flat base but after growth, or if the surface becomes damaged or compromised, such as from a skin wound, the tumor will ulcerate, bleed and appear to “hang” on a stalk (pedunculated) or become extremely invasive into the surrounding skin. They have the potential to develop at wound sites, particularly damage overlying limbs, and often take the appearance of infected granulation tissue.

   Found: Anywhere on the body and have the potential to develop quickly from verrucous or nodular sarcoids.

5. Mixed

   Appearance: Include a mixture of two or more types of sarcoids, often of different ages, forming a “colony.”

   Traits: It is common for horses susceptible to skin tumors to display mixed characteristics and to develop multiple sarcoid types in one region or the appearance of multiple sarcoid types at different sites around the body.

   Found: In any area, but they most often appear on the head, armpit and groin areas.

6. Malevolent

   Appearance: Extremely rare and the most aggressive type of tumor that spreads extensively from the original site through the skin and subcutaneous tissue.

   Traits: Sometimes confusingly referred to as “malignant” (because of their severity), but these tumors do not metastasize to internal organs. They can continue locally along lymph vessels producing cords of tumor tissue interspersed with nodules and secondary ulcerating fibroblastic lesions that tend to form into larger groups. Because this uncommon type can spread over a wide area and grow quickly, malevolent sarcoids can become quite difficult to manage. While some cases develop spontaneously, malevolent sarcoids can be the result of repeated incomplete or unsuccessful treatments.

   Found: Most commonly affect the face, elbow and inner thigh regions.

Sarcoid Treatment Options

• Surgical Removal

  Surgical removal is common and a viable option dependent on the location of the tumor. General anesthesia may be used, although local anesthetic is usually adequate, and a single or small number of sarcoids can be simply cut out. Nodular sarcoids often respond well to surgical removal. The wound can be stitched or left open to heal from the inside out forming a scab and usually resolving in four to six weeks. However, failure to remove the entire sarcoid will increase the chances of aggressive recurrence. For this reason, veterinarians usually include a wide surgical margin around the tumor. While the procedure is simple, the surgical excision failure rate is high with an over 80% recurrence rate with surgery alone, particularly without additional therapy. Cryotherapy is often used with surgical intervention and improves success rates. Benefits of surgery include a fairly quick healing time, good cosmetic results, and it can be effective in some difficult areas like the ears.

• Laser Surgery

  Laser surgery, a relatively new technique, is becoming more widely used. Where available, a laser removes the tumor as well as its base, along with a margin of healthy tissue to prevent re-growth. Because the tissues are burned, bleeding is minimal. Standing sedation is usually used with local anesthetic, or the horse may be put under general anesthetic. This treatment has success rates of over 80% and low risk, but healing and recovery can be a slow process with scar formation.

• Cryosurgery (Cryotherapy, Freezing)

  In cryosurgery, liquid nitrogen is used to rapidly freeze tissue and kill the rapidly dividing cancerous cells. This treatment is often used on small, occult-type sarcoids, and to prevent recurrence it is also used to treat the base and any remaining sarcoid tissue following a de-bulking surgery. Because hair follicles are damaged, patches of white hair usually develop at the treatment site. Cryosurgery can be time consuming, may require repeated treatments, and is not often a primary or preferred treatment option.

• BCG Injection (Immune Therapy)

  The BCG (bacillus Calmette-Guérin) injection works by local immune modulation. The BCG injection is produced from Myobacterium bovis, a bacterium actually used to immunize against tuberculosis. Essentially, BCG is directly injected into the sarcoid to stimulate the immune system and provoke a reaction to destroy or reject the tumor tissue. It is mostly used for sarcoids located near and around the eyes, especially nodular types. Multiple injections over several weeks or months are required. Heavy sedation is usually needed, and anti-inflammatory medication is given before each injection to reduce the risk of allergic reaction.

• Autologous Implantation

  Autologous vaccinations — autologous means “from the same individual” — are a common technique used to aid other livestock species. For equine sarcoids, a small sample of the tumorous tissue is taken, frozen in liquid nitrogen to kill the virus, thawed and implanted back into the horse’s body (usually the neck). The implant stimulates an immune response and uses the animal’s own immunity to recognize the tumor as foreign and attack it. Ongoing research is dedicated to this promising treatment.

• Chemotherapy

  Cisplatin and carboplatin chemotherapy drugs are injected directly into sarcoids and act by interfering with the DNA replication in tumor cells. These drugs can cause local inflammation and possible scarring. Treatment costs can be expensive and will likely require multiple doses over months dependent on the sarcoid.

• Electrochemotherapy (ECT)

  Electrochemotherapy combines the use of a chemotherapeutic (typically Cisplatin) drug with electric pulses to increase its effectiveness. High-voltage electric pulses open the cell walls allowing a significantly increased concentration of the drug to enter the cell and deliver a more potent dose. The procedure is brief, usually under 15 minutes, and requires general anesthesia. Recent studies have shown that the combination of surgical debulking of the tumor followed by ECT had very high success rates.

• Radiation (Radiotherapy, Interstitial Brachytherapy)

  Radiation has been shown to be a highly effective treatment for tumors that do not respond to traditional therapies, including lesions on the legs and around the eye. It may also be the best option for aggressive, recurrent sarcoids. This type of treatment is expensive and not widely available (usually offered at specialized hospitals), often requiring general anesthesia.

• Topical Treatments (Imiquimod (Aldara), bloodroot extracts)

  Topical treatments are used widely on sarcoids. These specific, veterinary-use only cytotoxic preparations that often contain anti-viral and anti-tumor ingredients, attack and kill abnormal tumor cells. They are often creams and can be very effective when used to treat smaller, flat occult type sarcoids, or as an adjunct treatment following the surgical debulking of larger sarcoids. Treatment time can be long, up to several months, and often the sarcoid will appear worse before it improves. Topical preparations can be painful with localized inflammation and swelling common and have the potential to damage healthy tissue. The treatments are not ideal to use on sensitive bony areas or places with concentrated nerve or blood vessels.