Pet Talk | Targeting cancer in cats

Pet Talk | Targeting cancer in cats

By JAKE SMILEY
UI College of Veterinary Medicine

Feline injection-site sarcoma (FISS) is an aggressive form of cancer in cats associated with the administration of vaccines and injectable medications. It affects as many as 1 in 1,000 vaccinated cats. This cancer was once thought to be a rare side-effect of rabies vaccines, but now experts believe it can occur following any kind of injection, even microchipping.

Dr. Elizabeth Maxwell, who has recently completed a residency in small-animal surgery at the UI Veterinary Teaching Hospital in Urbana, has been investigating one treatment option for FISS during her three years at Illinois.

"The current theory is that when a cat is given a shot, a chronic inflammatory reaction develops at the site of the injection, triggering abnormal transformation of cells," Maxwell said. "We know that FISS is treatable with surgical removal of the tumor, radiation therapy and with chemotherapy, but these approaches can be very aggressive, expensive for clients and risky for old or very sick cats. The best prognosis lies in surgery that often requires amputation or removal of part of bones or parts of the abdominal wall. Even then, it's always possible that the cancer can come back if a part of the tumor escaped notice or spread."

Carboplatin bead studied for FISS

Working with Dr. Heidi Phillips, associate professor of small animal surgery, Maxwell is investigating a cost-effective, local treatment option for cats with FISS.

Their research focuses on the chemotherapeutic drug called carboplatin. Carboplatin is used commonly in both dogs and cats to treat cancer but can be associated with kidney failure or gastrointestinal problems when injected into the bloodstream.

If carboplatin could be administered to the tumor without reaching other parts of the body, it might prove to be safer and a less expensive treatment approach than the current standards of care for FISS.

Maxwell and Phillips are studying whether a tiny clay-like bead containing carboplatin can be placed under the patient's skin, where the bead would dissolve and diffuse the drug into the tissues.

"Our hope is that by using the beads, the drug will affect only the tumor and the tissue around it and won't spread and damage the rest of the body, Maxwell said. "This procedure would also be minimally invasive and allow an affordable treatment option to use alone or in conjunction with surgery."

To test their idea, the doctors conducted a three-phase study at the College of Veterinary Medicine.

The first phase was to test carboplatin on cell cultures to ensure that it could kill the cancer cells.

In the second phase, the beads were placed in plates of agar gel, used as a model for cat tissue, to understand how the drug would spread.

The third and final phase involved placing beads in healthy cats to see how the beads and the drugs would affect the body.

The cats in this study did not have any reactions to implantation of the beads, and the chemotherapy drug was found to diffuse into the tissues around the beads.

Third phase tested safety

Why was the drug given to healthy rather than FISS-afflicted cats?

"We first wanted to ensure that the beads were safe to implant and wouldn't be absorbed in high enough concentration that it could affect their bodies," Maxwell said. "In the safety phase of drug development, it's important to minimize variables."

Maxwell and Phillips have already published two papers reporting the results of the first and second phases of their study and anticipate publication of the last phase later this year. They've also presented their findings at several conferences for veterinary surgeons.

The next step for evaluating the use of carboplatin beads to treat FISS will involve studying the efficacy of the beads for cats with this form of cancer. Maxwell hopes this approach might have applications for other types of cancers as well.

An archive of pet columns from the UI College of Veterinary Medicine is available at vetmed.illinois.edu/petcolumns/. Requests for reprints of this article may be directed to Chris Beuoy at beuoy@illinois.edu.

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