Meddleton Equine Hospital

A new mass or swelling on your horse should be seen by your Veterinarian if it is not resolving rapidly (insect bite), is growing, is causing discomfort, or is ulcerated. Swelling and nodules caused by insect bites or minor trauma will generally resolve rapidly without intervention. However, any new swelling that show no signs of resolving after one week of onset should be examined.

Tumors are common in the horse and can occur on haired skin, prepuce, penis, eyelids, eyeball, anus, perineum, and vulva. Specific locations or coat colors are associated with specific types of tumors. Frequently encountered examples are Melanomas around the anus in grey horses or Squamous Cell Carcinoma (SCC) of the eyelids of lightly pigmented horses.

Any new mass should be brought to the attention of your Veterinarian. Most new masses should be biopsied to determine what kind of tumor it is, and to plan the most appropriate treatment. The most frequently encountered external tumors of horses are Sarcoids, SCC, and Melanomas.

Sarcoids are benign (do not metastasize), but can be very problematic due to their locally aggressive nature. This is especially true for the eyelids and the limbs.

SCC can metastasize, but tends to do so slowly. The penis, prepuce, perineal area, eyelids, and eyeballs are the sites of predilection for this tumor.

Melanomas occur most frequently around the anus of grey horses, but they are also seen around the eyelids, prepuce, udder, lips, and salivary glands. Melanomas are almost always benign in grey horses, but can be aggressive and metastatic in non-grey horses. Although benign, perineal Melanomas should be treated to prevent problems associated with defecation as they grow.

Diagnosis

Diagnosis can occasionally be with a needle aspirate, but more frequently requires a biopsy. For small tumors, the biopsy can be curative (all the tumor is gone and should not return). For larger tumors, or for tumors occurring in areas that do not lend themselves to full surgical removal, other treatment modalities can be employed. The location of the tumor and the type of tumor will dictate what treatment or combination of treatments is most appropriate.

Treatment

If surgical excision is not feasible, cryosurgery is often the next treatment option. This involves freezing the tumor and surrounding tissue using liquid Nitrogen. This causes death of the tumor and surrounding tissue. The dead tissue, including the tumor, will fall off as a scab, and normal tissue will grow to fill the wound. This approach can also be used with caustic topical products; this is often used to address Sarcoids.

Injection of chemotherapeutic agents directly into the tumor has also been used to treat certain tumors. This is most commonly used for small tumors arising close to or on the eyeball. A new and promising approach to the treatment of equine tumors, especially in difficult areas, is the implantation of slow release chemotherapeutic delivery devices into the bed of the tumor.

In many cases, a combination of more than one of these modalities is indicated. An examination and biopsy will allow your Veterinarian to determine what treatment option is appropriate for your horse’s tumor.