October 8, 2007
By Deb M. Eldredge, DVM
“A vaccine for cancer” sounds like a line from a science fiction story, doesn’t it? As of March, it is a reality — for dogs, at least. The animal health company Merial, working with New York’s Animal Medical Center and Memorial Sloan-Kettering Cancer Center, has developed a vaccine that is now approved for use in treating canine oral melanomas
Canine melanoma is a cancer in dogs that is associated with cells called melanocytes. Typically these cells are pigmented, but they can be amelanotic or pale. The cancer can be seen in nail beds, on feet and in the skin but tends to be most aggressive in the oral or mouth area. It is the most common oral tumor in dogs.
Traditionally, treatment for melanoma has consisted of surgery to remove as much of the growth as possible followed by radiation to catch any remaining cells. According to Dr. Nicole Leibman, a veterinary oncologist with the Animal Medical Center, chemotherapy has not been very effective. Sadly, oral melanomas have often spread or metastasized to other parts of the body before the growth has been noticed.
Canine melanomas are classified into stages by the World Health Organization protocols. Stage I growths are small and show no evidence of having spread. The stages then escalate to Stage IV, with each stage being progressively more serious. In Stage IV, the cancer is larger and there is evidence of distant spread in the dog’s body. Using the standard treatments, dogs with Stage II melanoma generally survive less than five months, and dogs with Stage III or IV melanoma often only live two to three months.
Now, with this new and exciting vaccine, these dogs are treated postsurgically and may survive up to a year or more. The routine procedure is to give four doses of the vaccine every other week after the cancer has been reduced by surgery and radiation therapy. Boosters of the vaccine are then given every six months after that.
How does this vaccine work?
“We think of vaccines as injections to prevent problems, not to cure them,” says Dr. Leibman. “But the immune system can be manipulated to attack deadly cells as well as outside invaders like bacteria and viruses.”
Tyrosinase is a protein produced by melanomas. The goal was to find a way to stimulate a dog’s body to react against the tyrosinase protein but not stimulate a widespread autoimmune reaction against other normal cells in the dog’s body. The body has many safeguards in place to prevent attacks on its own cells by its own immune system. Researchers found that human tyrosinase is just different enough from canine tyrosinase to stimulate an immune response, but close enough to the canine version so the immune response is directed against those canine melanoma cells with the protein. So basically, the vaccine uses human tyrosinase DNA to stimulate your dog’s own body to fight the cancer.
At this time, the vaccine is approved only for use via board-certified veterinary oncologists, so your veterinarian may have to refer your dog for treatment. Also, the vaccine is approved only for treatment of oral melanomas — not for prevention — even in breeds that are predisposed to this cancer. It is also not currently approved for use on any other cancers, including melanomas in other areas, though anecdotally the vaccine may help those too. The vaccine is intended only for use after the cancer reduction treatment by surgery or radiation has been done, so that the dog’s immune system has less work to do.
Adding to the high-tech aura surrounding this vaccine is a new method developed for its delivery. This is a special transdermal delivery system that does not use a needle. Instead, a pressure system puts the vaccine directly into the muscle in a wide distribution pattern.
What are the potential future ramifications of the vaccine?
“We’re happy that the work we do in conjunction with Memorial Sloan-Kettering may be helpful in advancing treatment in people for this disease,” says Dr. Leibman.
Another example of how man’s best friend shows us the way — people and dogs helping one another to fight cancer.
Dr. Deb M. Eldredge graduated from Cornell University as the first recipient of the Gentle Doctor Award. She has been in private practice and is active in virtually all dog sports. She is also an award-winning writer — her book “Cancer and Your Pet” was a finalist in the Dog Writers Association of America (DWAA) contest, and “Head of the Class,” a training book written with her daughter, won the Best Training and Behavior Book Award from DWAA in 2006.
