Tagamet, a human ulcer drug, proves effectiveMelanoma, skin cancer involving the pigment-producing cells of the skin, is especially common in gray horses and has been recognized for many years. These black tumors appear most often under the tail, around the vulva, or on the external male genitals. The lumps may appear singly or in groups and may develop slowly or rapidly.
Rapidly growing lumps often indicate malignancy that may spread internally to the liver, spleen, lungs, or other vital organs.
Many medical and surgical treatments have been tried for melanoma, with varying success. All too often results have been disappointing. During the past decade, however, more hopeful results have been obtained with cimetidine, whose brand name is Tagamet. This medication, developed in the mid-1970s, is used to treat human ulcers.
Doctors observed that human melanoma patients who were also taking Tagamet for stomach ulcers experienced remission of their cancers. Dr. Tom Goetz of the University of Illinois decided to try this drug on a gray Lipizzan gelding who had many small melanomas that had spread from under his tail to his belly and up his back. The tumors had been multiplying over his body during a three-year period. A single large tumor on his back had been irritated by use of a saddle and would not heal.

Oral doses
The experimental treatment by Goetz consisted of oral doses of Tagamet three times daily. After one month of treatment, the fastest-growing tumor had healed, was no longer raw and bleeding, and had shrunk to one-third its earlier size. After three months of treatment, this tumor vanished completely, and the skin healed up and looked normal. In addition, the lumps under the tail and on the belly had decreased in size and number.
Treatment with Tagamet was halted after one year because by that time there was very little additional change in the appearance of the remaining growths. After 312 years, no new growths had appeared, and the remaining old tumors had not enlarged.
Because of this remarkable success, other veterinarians began using Tagamet to treat melanomas in horses, and several studies were done. The results of these studies on Tagamet treatment for equine melanomas were published in the February 1, 1990, issue of the Journal of the American Veterinary Medical Association. Since that time, more veterinarians have been treating melanomas in this way.

With other treatments
While its success rate is not 100%, the use of Tagamet in conjunction with other treatment methods (including surgical removal, with follow-up cauterization or freezing to kill any remaining cancer cells) can provide a more favorable prognosis than in the past.
For instance, one 24-year-old Thoroughbred broodmare had been retired because her entire pelvic area was filled with melanoma growths that had spread from one ulcerated two-inch tumor under her tail. After three months of treatment with Tagamet, there were no internal tumors, her pelvic area was normal, and the original lump under her tail had shrunk to one inch in diameter and was healing up.
The Tagamet treatment, which should be done only under the supervision of a veterinarian, may become cheaper if less expensive generic drugs are available. This ulcer medication seems to work best on horses with rapidly growing tumors that become soft or oozing. It has been theorized by researchers that cimetidine shrinks the tumors by encouraging the horses own immune system to fight the cancer.
The drugs effect is fairly long-lasting. Usually, 3-to-4 months of treatment is adequate. Once the horses immune system is stimulated to fight the tumors, the horses body seems to have control over the cancer for several years. In older gray horses afflicted with melanoma, one round of treatment may be enough to put the cancer into remission for the rest of the horses life.