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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.
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.
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
Nodular Sarcoids - These often present as many solid nodules of multiple sizes. Like verrucose sarcoids these may ulcerate
Mixed Sarcoids - In many cases horses with present with a variation of two or more of the above types
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.
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.
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.
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.
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