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What You Should Know about Injection Site Sarcoma

By: Chris Cosgrove

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Ten years ago, Colleen Hahn saved the life of a kitten that had been placed with her littermates in a bag and tossed into a canal near West Palm Beach, Fla. Today, she is struggling again to keep the cat alive – this time against a medical problem that strikes fear and uncertainty into the hearts of cat owners.

Hahn's cat, named Kazy, has been diagnosed with injection site sarcoma, a cancerous, often fatal tumor that veterinarians believe is caused by routine vaccinations for rabies and feline leukemia. Dogs are not affected.

The disease is believed to affect between one and three cats out of every 10,000 cats that are vaccinated and maybe even as many as one of every 1,000. Those are small odds but they are enough to make pet owners and veterinarians weigh the risks and benefits of getting the vaccinations, particularly for older animals.

Veterinarians aren't certain how vaccines cause the tumors, but they believe that the vaccinations somehow trigger an overzealous immune system response in cats that may be genetically susceptible.

Kazy's Story

Hahn took Kazy and her two other cats in for regular vaccinations, and all three received the same shots between the shoulder blades. A little more than six months later, Hahn noticed a lump between Kazy's shoulders, but it disappeared. A few months later, she noticed a more pronounced lump in the same spot. When it continued to grow, Hahn called her veterinary clinic, but the receptionist told her that if Kazy was eating well and seemed healthy she could probably wait a few weeks until her regular appointment to bring her in. Within a week the lump had doubled in size.

"It was about an inch and a half in diameter and 2 inches high. When I saw that, I knew I was in trouble," said Hahn. "This time when I called, I talked to the vet, and he knew immediately what it was and sent me directly to a specialist."

Hahn now looks back tortured by the fact that the attentive medical care she gave Kazy may end up costing the cat her life. And thousands of cat owners share the fear that their efforts to keep their cats healthy could produce similar tragic results.

What Should You Do?

Veterinarians are certain that cats need to undergo a course of vaccinations and booster shots from the time they are kittens through 2 years of age. These are designed to keep cats from falling prey to infectious diseases that once were far more prevalent than they are today. Rabies vaccinations are often required by law.

When your cat reaches 3 years of age, you should discuss the benefits and risks of annual vaccination with your veterinarian. Some veterinarians believe that annual re-vaccination is an important and critical part of preventative health care. Others believe that there is little scientific information to show that annual re-vaccination of older cats is necessary for some diseases. Immunity to many viruses probably persists for the life of the animal.

There is no nationally accepted standard at this time, leaving it to veterinarians and pet owners to decide the best course of action. Dr. Philip Kass, associate professor of epidemiology at the University of California at Davis School of Veterinary Medicine, pointed out, for example, that a cat has a very low risk of contracting feline leukemia if kept indoors all the time.

"If I had an indoor cat, I would probably not give it the feline leukemia vaccination," said Dr. Kass. For cats that go outdoors, however, the risk of feline leukemia is still greater than that of acquiring injection site sarcoma.

When to Vaccinate

The American Association of Feline Practitioners has suggested shifting to vaccinating cats every 3 years instead of yearly. Some veterinarians prefer breaking this down into one shot a year so that cats can still have the benefit of annual examinations.

In other words, veterinary medicine does not yet have all the answers – even about how prevalent injection site sarcoma is. "It's hard to pin down the exact number because these tumors often occur a long time after the injection," said Kass.

Confounding the problem, cats that have not been vaccinated may also develop the same type of cancerous tumors, making it difficult to ascertain which tumors are linked to vaccination and which develop for other unknown reasons.

Treating Injection Site Sarcoma

A sarcoma is a malignant tumor composed of cells derived from connective tissue. These tumors often develop quickly and can spread, or metastasize, to other parts of the body. There currently are no uniformly successful treatments for injection site sarcomas, but treatment can include a combination of surgery, radiation treatment and chemotherapy.

Hahn considered all those options at costs ranging from $1,500 to $6,000, as well as letting the disease progress and euthanizing Kazy if it became necessary.

"My concern all along was the quality of life for Kazy," said Hahn, explaining why she rejected chemotherapy, a commonly used treatment that is well tolerated by many animals. "If I were to drive her to chemo every day, her understanding of this would be that I was driving her to be tortured. I felt it would just be too stressful for her."

Hahn's first thought about surgery was that an aggressive attack and its after effects would be very hard on Kazy. She consulted a surgical oncologist, Dr. Charles Kuntz, about removing only part of the tumor to buy Kazy some time and make her more comfortable. But Kuntz convinced Hahn that a halfway measure would accomplish very little. She agreed to let the surgeon try to remove the tumor, but decided that if it had spread too far she would have Kazy euthanized.

Kazy Lucks Out

Luck was on Kazy's side again, just as it had been 10 years ago when Hahn fished her out of the canal. Kuntz successfully removed the tumor along with 5 centimeters of tissue all around the tumor that was not cancerous. Removing the tumor with 5 centimeters of "clear margins" doesn't guarantee that Kazy is cured, but Kuntz believes this aggressive kind of surgery that takes more than the traditional 3 centimeters may very well be the best chance for a cure. He said that of the 40 cats he has operated on in the past two years to remove injection site sarcoma tumors, only one has had a recurrence of the disease.

"I believe a lot of these cats can be cured," he said, particularly if the lump is caught early.

Hahn was thrilled with the outcome. "Kazy looks God-awful - like something in a science experiment. She's in a body stocking and she's got staples in a big 'X' from her shoulder blades to her back legs, but they let me take her home two days after the surgery and she's eating her favorite yogurt and acting bright and chipper," she said.

Lessons Learned

Although Hahn describes herself as an animal person - in addition to three cats, she has birds and horses - she had never heard of injection site sarcoma. She learned the hard way and now believes veterinarians should post notices or hand out brochures about the disease. And she stresses the importance of finding a specialist to treat a cat that develops the disease.

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What You Should Know about Injection Site Sarcoma




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