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What are Skin Tumors?

Although other types of tumors may occur, the three most common skin tumors seen in horses are sarcoids, melanomas, and squamous cell carcinoma. These tumors are often diagnosed from visual assessment and may present as anything from flat masses to large pedunculated tumors. In order to increase the chance of full recovery and decrease the risk of metastasis it is vital that you contact your veterinarian for treatment promptly.

Skin tumors are common in horses all breeds, although these tumors show more prevalence in adult or geriatric horses. These tumors present a low risk of metastasis as are slow to spread to other areas of the body.

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Symptoms of Skin Tumors in Horses

The symptoms seen in horses may vary depending on the type of skin tumor affecting them. These may be anything from small, wart-like growths, to large fleshy tumors. These frequently become ulcerated and may become infected in some cases. 

  • May be circular flat tumors
  • Solid nodules could be present
  • Could also be fleshy
  • May be flat
  • Raised masses may be evident
  • Color could be black
  • Difficulty urinating or defecating may indicate metastasis

Types

Sarcoids

Sarcoids are the most common type of skin tumor in equids, making up to 36% of all skin tumors in equids. These tumors can affect horses of any age, however there are breed predispositions and are most common in Quarter Horses and related breeds. Sarcoids are broken into six main forms.

  • Occult Sarcoids - These are often circular, flat tumors with localized alopecia
  • Verrucose Sarcoids - These have a small, wart-like appearance and may ulcerate and bleed; these can cover large areas of the horse
  • Nodular Sarcoids - These often present as many solid nodules of multiple sizes. Like verrucose sarcoids these may ulcerate
  • Fibroblastic Sarcoids - These are usually large, fleshy tumors with wet, hemorrhagic surfaces which cause them to bleed easily
  • Mixed Sarcoids - In many cases horses with present with a variation of two or more of the above types
  • Malevolent - This is a very rare and aggressive form of sarcoid in horses that spreads throughout the horse

Melanomas 

These are most prevalent in geriatric horses. These are commonly seen in grey horses, and have a higher likelihood of malignancy in non-grey horses. 

These appear as raised masses which may be underneath healthy appearing skin or appear black. The most common sites for melanomas in horses are the eyelids, throat and around the hind quarters, particularly the tail and perineum as well as the sheath in male horses. 

Squamous Cell Carcinomas

Squamous cell carcinomas are common masses seen in all mammals, particularly older, white cats. In horses these are seen in adult or geriatric horses and show no breed disposition, however are most commonly seen on the un-pigmented areas of the animal such as the eye and urogenital structures. These generally have the appearance of proud flesh or ulcerative masses.

Causes of Skin Tumors in Horses

  • Age
  • Sarcoids are common in Quarter horses
  • They may form at areas where skin wounds have occured recurrently
  • Sometimes will form where the girth and bridle have been
  • It is more common for grey horses to get melanoma
  • Can be seen on eyelids and tail area
  • Squamous cell carcinoma can be seen on white or pink skinned areas

Diagnosis of Skin Tumors in Horses

Your veterinarian will examine your horse, carefully checking over the skin for signs of other lumps or masses, or infection due to ulceration. Symptoms such as difficulty urinating or defecating may indicate metastasis has taken place, and indicate the need for more invasive treatment. Your veterinarian will also assess the temperament of your horse, an easy to handle horse may be able to have complete removal of the tumor under limited anesthetic restraint.

Treatment of Skin Tumors in Horses

The best treatment for your horse will depend on the type of tumor and location. Commonly used treatments for removal include surgical or laser excision. In some cases, further treatment such as cryotherapy, radiation therapy, or chemotherapy drugs may be required. 

If surgical excision is performed your veterinarian will remove the lump and attempt to leave margins of up to 1cm, this reduces the risk of the lump returning. Due to the importance of clean margins for successful removal areas that prevent this, such as the limbs or eyes, may have reduced success rates or require further treatment such as radiation therapy. 

If your horse has a pedunculated sarcoid with a discernible neck it may be possible to ligate the tumor with rubber bands or suture material.

Recovery of Skin Tumors in Horses

The prognosis for your horse will most likely be good following early treatment and successful surgery. Your horse will need supportive care following surgical excision; this may include bandaging, stall rest or exercise restriction. Your horse should be offered high quality food that meets all their nutritional needs and supports their immune system and recovery. 

Unlike humans who experience severe side effects during radiation therapy, horses maintain excellent life quality throughout treatment. In order to increase the likelihood of successful treatment your veterinarian may advise radiation or chemotherapy treatment is given.

Factors that may reduce the chance of full recovery is incomplete removal of the mass, poor management post surgery which leads to infection or trauma, or late treatment that resulted in metastasis.