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patients die within six months to a year of onset.
Melanomas in horses act very differently. They are usually only locally invasive and are slow growing. These round, black nodules are commonly found near the base of the ears, around the eyes, around the neck and jugular groove (the indentation on the side of the neck where the jugular lies between muscle groups), under the tail and around the vulva or rectum. These lumps are generally smooth, hard and non-painful. Occasionally, equine melanomas can metastasize and cause devastating internal problems, but most tumors remain in the skin and grow slowly during the horse's lifespan.
Diagnosis is made by taking a piece of the mass and examining it under a microscope. The characteristic dark, black granules of melanin within the tumor cells confirm the disease.
If the lump is small and not causing any other problems, it is usually best left alone. Some equine surgeons argue that operating on melanomas "activates" the cells and increases the chances of tumor growth. They recommend a cautious approach to the problem.
Large masses that interfere with tack or prohibit horses from defecating, for example, have to be treated.
Laser surgery has really helped in the surgical approach to melanoma management because it has enabled veterinarians to remove melanomas located in areas that would be difficult to operate on using traditional techniques. The laser cuts and seals blood vessels and makes dissection easier in areas where there is not a lot of extra skin, such as under the tail.
Medical management of melanomas is the more traditional approach. Cimetidine (Tagamet) is a drug commonly used to treat stomach ulcers in horses and humans. This drug also has a potent effect on some melanomas and, while not curative, will drastically reduce the size of melanomas throughout the body.
Researchers have developed a tissue-based vaccine made from the horse's own tumor cells. Good re-sponses have been obtained for mel-anomas on the face, body and legs; tumors on the tail/vulva and along the jugular do not respond as well.
Additional anti-cancer drugs and treatments, such as radiation, are
currently being developed. In the future, gene therapy may enable us to manipulate genetic signals to prevent cells from becoming cancerous, or turn off cancer-like functions once they begin.
Ken Marcella, D.V.M., is based at the Chattahoochee Equine Center in Canton, Ga.
A Switch in Time
Researchers at Cornell University have made use of the ongoing inquiry into the genetic structure of the horse.
Dr. Richard Cerione, a professor of molecular medicine at Cornell, has announced the discovery of a particular protein complex that is thought to influence the malignant transformation of cells in the production of some types of cancer. The body is constantly producing new cells to replace older ones and to help in growth and development. Cancers occur because something goes wrong in the development of new cells. Instead of producing a new, healthy cell, some defect in the transformation or reproduction process occurs and a malignant or cancerous cell is produced. Cerione and his group believe they have found the genetic switch, Cdc42, that converts normal cells to cancerous cells.
If Cdc42 is indeed a controller of the pathway for cell development, it may open the door to an entirely new method of cancer treatment and control. Researchers believe that Cdc42, along with another molecule called GDI allow normal cells to develop or switches to make these cells become cancerous. Control of the switch molecule would allow doctors to turn off the production of cancer cells or, better yet, to block their production in the first place.
As more is learned about genetic function, more of these cellular switches that will help to keep bodies healthy and keep disease at bay may be discovered.
Preventing Laminitis In Horses
By Drs. Richard Mansmann and Christine King
Preventing Lameness in Horses is a small, affordable book that gets right to the point about the causes of this potentially devastating foot condition and how to prevent it.
Laminitis-the breakdown of the bond between the hoof wall and the coffin bone-is complex. The two authors explain the events that lead to laminitis. The text is further enhanced by boxes containing additional explanations and related points of interest.
In the second section, Mansmann and King explain why factors such as breed (ponies, Morgan, donkeys and thoroughbreds), age and activity level (inactivity, concussion, exhaustion and so forth) can increase the risk. According to the book, endophyte-infected fescue, black walnuts, excessive selenium, even cortisone can contribute to laminitis. This section provides details as to what signs to look for should you suspect a laminitis problem.
The third part of the book presents management strategies to help prevent laminitis in the first place. Practical suggestions include limiting time on lush pasture (especially for ponies), fencing off portions of the pasture and using a grazing muzzle.
The authors provide ways to assess your horse's susceptibility based on the number of risk factors that apply, and there is a page devoted to emergency instructions should you suspect your horse has laminitis.
This paperback has plenty of easy-to-understand illustrations and diagrams. It is designed to be an informative, quick read. It's also a good book to have on the tack room shelf in case you suspect the worst. Because so many ponies tend to founder, this is a good addition to the libraries of young owners.
-Rebecca Colnar
Preventing Laminitis in Horses, $11.95 plus $2 handling, is available from the Paper Horse, PO Box 1771, Cary, NC 27512 or www.paper-horse.com.
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