Common Equine Skin Cancers: What You Need To Know.


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Common Equine Skin Cancers: What You Need To Know.

Understanding Equine Skin Cancer

The word “cancer” lingers in the back of the mind of any caring equine owner when his or her horse develops a skin condition. There are a number of common equine skin cancers which are benign and will not metastasize, (This means that the cancer may spread within the horse's body.) whereas others are more aggressive and may require urgent attention. Many tumors can be successfully treated with the right treatment by your veterinarian and correct nursing support at home. This article discusses three of the most frequently observed skin cancers in horses and gives you an idea of what symptoms to watch out for. As with any condition we talk about here at Spalding, early diagnosis is important and if you are ever concerned about your horse’s health it is important to talk to your vet.

Melanomas in Horses

Most commonly found in grey horses or those with pale muzzles, melanomas are slow-growing and benign growths that rarely cause serious problems. However, in some horses, they can become an issue if found in pressure points, i.e. where they impede movement or are liable to create chaffing when the horse is tacked up.

Melanoma in horse
Grey Horse with a melanoma

The first symptom is usually a firm, grey or black mass on the horse’s body, normally beginning as a small solitary nodule beneath the skin which can develop into other nodules over an undetermined period of time (often years). In some cases, the growths join up to form a multi-nodular mass that can cause skin ulcers. Melanomas are most commonly found:

  • under the tail and around the genitals/anus
  • on the head below the ear and behind the jaw bone
  • on the limbs and neck
  • Occasionally on the eyelid or within the eye.


Treatment varies according to the type of the melanoma and its location. Small growths are often successfully treated by surgical removal but in some cases this is difficult, owing to the size or position of the mass(es). Cryosurgery (freezing) has been used with varying results and the treatment often has to be repeated. Other methods of treatment can include radiotherapy and chemotherapy, again depending on the size of the growth and the veterinarian’s recommendation. There is no guaranteed method of removal for melanomas and it is always important to call your veterinarian, should any growths begin rapidly changing in appearance.

Squamous Cell Carcinomas

squamous cell cancer in horse
Squamous Cell Carcinoma Surgery

This is an aggressive and invasive type of tumor but it can often be removed by localized surgery. Squamous cell carcinomas can affect skin mucosae (lining), sinuses and certain areas of skin, namely the external genital region of the horse and around the eyes, including the cornea and third eyelid. Horses with large areas of white hair or non-pigmented skin are more susceptible to this type of growth and it can be a result of UV damage from the sun.

Tumors are often solitary and somewhere between dark pink and light red in color. They can be bumpy, soft to the touch and moist.

Squamous cell carcinomas are always serious and require treatment by your veterinarian. Surgery is normally required to remove abnormal tissue, and will often necessitate removal of a large area of healthy skin as well. This is in order to remove enough tissue to ensure that tumor cells are completely eliminated and that the remaining tissue is surrounded by a “margin” of normal cells to allow for optimal healing and new growth.

In some cases, it may not be possible to remove the tumor and so supplemental therapy will be recommended. This can include chemotherapy, cryotherapy, radiation therapy or photodynamic therapy. In some cases, a topical chemotherapy drug will be prescribed in the form of drops (for tumors near the eye) or cream (for tumors in other parts of the body).


We have previously discussed sarcoids, in an earlier article on the diagnosis and treatment of these skin tumors, the most commonly found skin growth in horses. They are categorized into six types (occult, verrucous, fibroblastic, malevolent, mixed and nodular,) and are caused by a virus that is spread by flies. They vary in appearance, from hairless nodules and solid, thickened warts to large, ulcerated clusters.

Sarcoid in horses

Although sarcoids can affect any part of the body, classic sites in which they are found are around the horse's eyes, ears, legs and abdomen.
The exact cause is still unknown and in a large number of cases, it may be best to leave the sarcoids alone as they most likely will not change or develop.

However, when lesions are directly underneath tack or have become sore, they will require veterinary attention.
Your veterinarian may elect to biopsy the tumor to identify it accurately. Treatment can involve surgery, chemotherapy or laser removal but, as with melanomas,
treatment may not always be effective or long lasting and the sarcoids may grow back.

Skin growths are common in horses and knowing the difference between types and their respective appearances and prognoses can help you quickly assess when it's best to call the veterinarian.

For more information on recognizing equine illnesses, come back to Spalding-Labs again soon!

*Image courtesy of wikimedia commons