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Also Known As

Growths, Neoplastic masses, Cancer - when malignant


A tumor is defined as an abnormal mass of tissue that continues to grow and is unresponsive to the bodies' influences that control normal cell growth. Usually, this label is applied to any masses that cause swelling in and on the body and may result from a wide range of causes.

Skin tumors in horses are relatively common in all breeds and at all ages. The three main types are sarcoids, melanomas, and squamous cell carcinomas. The main concern with skin tumors is that they will metastasize and affect other parts of the horse's body.

Tumors that originate in the horse's glands and organs are less common and more difficult to diagnose. Lymphosarcoma occurs most frequently, followed by stomach cancer.

The oral cavity, nasopharynx, kidney, adrenal gland, pituitary gland, bladder, liver, colon, bone, udder, and ovaries are also subject to tumors that may be cancerous growths. Unfortunately, most internal cancers do not produce symptoms until they are quite large and difficult to treat effectively.


  • Nodules or growths on the skin
  • Patches of hair loss
  • Scaly skin patches
  • Ulcerated areas
  • Lethargy
  • Colic-like symptoms
  • Altered metabolism


Causes vary, depending on the type of tumor. Most sarcoids appear to be caused by an interaction between the papilloma virus, that causes warts in cattle, and the genetics of the horse. The cause of melanomas is unknown, but because they affect gray- and light-colored horses, some connection is thought to exist between sunlight exposure and genetics, although research has not drawn direct links. Squamous cell carcinoma is thought to be caused by ultraviolet radiation and exposure to tumor-causing carcinogens.

Tumors in the organs and glands of horses become more apparent as horses age. Environmental factors, including carcinogens in feed, pastures, stables, and barn areas are the most likely culprits behind these tumors. In addition, skin cancers may metastasize and spread throughout the horse's system, including organs and glands.


Tumors are difficult to prevent, but frequent and routine inspections to catch growths in their earliest stages can minimize their affect on the horse's health. A veterinarian should evaluate any neoplastic masses and can recommend biopsies and treatment of any suspicious nodules that may be observed.

Good horse management, including proper feed and plenty of clean water, clean and sanitary living conditions, plus limiting exposure to too much sun will also help minimize the incidence of tumors.


Based on evaluation, and possibly biopsies, of a tumor, the veterinarian can determine the best treatment, taking into consideration the condition and age of the horse. If the tumor is thought to be invasive, surgery may be recommended. In other cases, the veterinarian will recommend treatment based on the specific type of tumor, its tendency to metastasize, where the tumor is located on or in the horse's body, and the general prognosis for the horse's future health.

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EquiMed Staff

EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.