Conscientious breeders and pet owners have been microchipping their cats for identification purposes for some time now. Indeed, microchipping pets is quite routine, with veterinarians often doing it as a matter of course when pets are brought in for spay or neutering. The microchip is used for identity purposes, returning lost pets to their owners, confirming identity for pet passports, genetic testing and registration purposes.

A widely reported case of a dog that seemingly developed a tumor at the site of its microchip implant has recently raised concerns over the possibility of tumors being linked to the use of microchip implants. Now some breeders are re-examining their microchip policy. Are microchips safe?

Reviewing The Literature Concerning the Occurrence of Cancer in Mice with Microchips

Dating from the mid-1990s, various studies reported that microchip implants have been implicated in "induced" malignant tumors in some lab mice and rats.

Studies published in veterinary and toxicology journals between 1996 and 2006 showed that lab mice and rats injected with microchips sometimes developed subcutaneous "sarcomas" - malignant tumors - most of them encasing the implants.

• In 1997, a study in Germany found cancers in 1 percent of 4,279 chipped mice. The tumors "are clearly due to the implanted microchips," the authors wrote.
• A 1998 study in Ridgefield, Conn., of 177 mice reported cancer incidence to be slightly higher than 10 percent - a result the researchers described as "surprising."
• A 2006 study in France detected tumors in 4.1 percent of 1,260 microchipped mice. This was one of six studies in which the scientists did not set out to find microchip-induced cancer but noticed the growths incidentally. They were testing compounds on behalf of chemical and pharmaceutical companies; but they ruled out the compounds as the tumors' cause. Because researchers only noted the most obvious tumors, the French study said, "These incidences may therefore slightly underestimate the true occurrence" of cancer.

Because none of the studies had a control group of animals that did not receive microchips, the normal rate of tumors could not be determined and compared to the rate with chips implanted.

Response From The Veterinary Profession

Dr. Cheryl London, a veterinarian oncologist at Ohio State University, noted: "It's much easier to cause cancer in mice than it is in people or pets. So it may be that what you're seeing in mice represents an exaggerated phenomenon of what may occur in other species."

Dr. George Demetri, director of the Center for Sarcoma and Bone Oncology at the Dana-Farber Cancer Institute in Boston stated that even though the tumor incidences were "reasonably small," in his view, the research underscored "certainly real risks".

Bottom Line

Millions of domestic pets have been implanted with microchips, without reports of significant problems. Tens of thousands of dogs have been chipped and veterinary pathologists haven't reported outbreaks of related sarcomas in the area of the neck, where canine implants are most often done.

In deciding to use microchips with our cats, as with many procedures, we must consider the benefit to risk ratio. It would seem that statistically, the benefits of microchipping well out-weighs the possible risks. It remains for each cat owner or breeder to make the best decision for their cats.