Sarcoids

What are sarcoids?

Sarcoids are locally aggressive, non-metastatic skin tumors. They are the most diagnosed tumors in equids and can affect equids of any age or sex. Sarcoids are associated with bovine papillomavirus -1 and -2, but this association is not well understood, and environmental and genetic variables are important in individual cases. Sarcoids have a high recurrence rate after treatment.

Although not contagious to other horses, a sarcoid can be transferred mechanically to a different part of a horse’s body by chronic rubbing with an ulcerated lesion. This type of sarcoid is locally invasive, destroying adjacent tissues, and should be managed as a malignant tumor. Advanced sarcoids occasionally can spread through the lymphatic system.

Six clinical forms of sarcoids are recognized. From mild and stable to severe and highly invasive, they are: 

• Occult – circular, flat, hairless
• Verrucose – scabby, solid nodules that can form over large areas
• Nodular – multiple solid nodules of various sizes that can become ulcerated and bleed
• Fibroblastic – fleshy lesions that bleed easily
• Mixed – have characteristics of one or more forms
• Malignant (malevolent) – rare, aggressive form that can spread extensively 

Many cases have features of more than one type (i.e. mixed).

What are the clinical signs of sarcoids?

The clinical signs of sarcoids can vary in the early stages from an almost circular area of hair loss with a gray, scaly surface, to a wart-like growth presenting as a skin thickening or small growths on a stalk. Common sites for sarcoids are the skin of the head (eyelid, ears, and mouth), neck, legs, and abdominal region, along with any previously traumatized sites.

Advanced sarcoids, also referred to as nodular or lumpy, may appear as a large mass with a surface that progresses from scaly and hairless to ulcerated. 

How are sarcoids diagnosed?

It is difficult to diagnose sarcoids visually as they can resemble other skin conditions. Histological evaluations can identify characteristic features of sarcoids that lead to a definitive diagnosis. The presence of bovine papillomavirus DNA is not sufficient for diagnosis.

How are sarcoids treated?

Equine sarcoids are notoriously difficult to treat and effective treatment varies by case. The location, number, and type of sarcoids usually guide treatment decisions. Treatments can be lengthy and expensive. Recurrence after treatment is common.

These tumors are usually considered benign and often do not cause any problems, at least initially, to affected animals. Unfortunately, this means that they are often allowed to progress to advanced stages, at which point they are difficult to treat.

Many treatments have been developed, including surgical removal, radiotherapy, chemotherapy, and immunotherapy. Large tumors may require treatment with multiple approaches.

As with all forms of cancer, the key to successful treatment is early diagnosis. Regular grooming and care of the horse will reveal any small lumps or bumps; these should be treated seriously and examined by a veterinarian. 

What is the prognosis for horses with sarcoids?

The prognosis for horses with sarcoids varies. These tumors are rarely metastatic. However, they can be locally aggressive and have significant health effects if they become ulcerated and/or infected.

How can sarcoids be prevented?

There is currently no clear way to prevent sarcoids in equids. Research on vaccination and immunotherapeutic treatments is ongoing.