A report published on Saturday by the Associated Press links RFID implants to cancer in laboratory animals.

But Kevin Warwick, professor of cybernetics at the University of Reading, England, and known for having RFID chips implanted in his body for short periods in 1998 and 2002, expressed skepticism about the studies cited in the AP report and questioned the ethics of Dow Chemical and its researchers for not publicizing their findings sooner.

"From both technical and medical viewpoints I am very surprised by this information and I question the validity of it," Warwick said in an e-mail. "Most (if not all) RFID implants are silicon encased and hermetically sealed -- there can therefore be no question of a materials problem. As pointed out in the article, in practice many animals have had such implants in place for several years now (quite a few humans, too) and I have not heard of one single case of there being a problem."

VeriChip, which makes RFID implants as medical devices to monitor human health, also took issue with the studies. "Over the last 15 years, millions of dogs and cats have safely received an implantable microchip with limited or no reports of adverse health reactions from this life-saving product, which was recently endorsed by the USDA," the company said in a statement posted on its Web site. "These chips are a well-accepted and well-respected means of global identification for pets in the veterinary community. Veterinarians would not continue to prescribe pet microchips if they believed they presented significant risk of malignant tumors in dogs and cats."

VeriChip cited two studies that find no link between RFID implants and cancer in mice. "Since learning of the [AP] article, we have discovered two studies from our manufacturer -" Chronic Evaluation in Rodents to a Microchip Implant Used for Animal Identification [D.J. Ball, R.L. Robinson, R.E. Stoll and G.E. Visscher, Sandoz Research Institute, East Hanover, N.J.] and Tissue Reaction to an Implantable Identification Device in Mice [Ghanta N. Rao and Jennifer Edmondson] -- that examine microchip implants in laboratory mice and rats and conclude that microchip implants DO NOT cause malignant tumors."

"We recognize we have a corporate responsibility to review these studies, to look at other studies, to do new studies if necessary, and do what it appropriate after reviewing all of the information in all regards, and we intend to do this," said Scott Silverman, chairman and CEO of VeriChip, during an ABC News interview broadcast on Good Morning America on Monday.

The AP report says that studies in veterinary and toxicology journals published between 1996 and 2006 found that "chipped" laboratory mice and rats sometimes developed tumors under their skin, most of which encased the implants.

The studies cited include: a 1998 study in Ridgefield, Conn., of 177 mice that found an incidence of cancer that surpassed 10%; a 2006 study in France of 1,260 "chipped" mice that found tumors in 4.1% of the mice; and a 1997 study in Germany that found cancer in 1% of 4,279 chipped mice.

While the AP report cautions against using these results to predict the effect of implantation on human health and notes that none of the studies included a control group of mice without implanted chips, several cancer researchers interviewed for the story nonetheless said the findings brought to light by the AP were enough to make them wary of RFID implants.

Warwick, however, remains unconvinced. "Ordinarily in life most people are affected by radio signals, of the type in question, every day -- yet there has not, to my knowledge, been any question that radio waves cause cancer," he said. "I can only conclude therefore that (a) these results are simply bogus, (b) possibly there is an attempt at industrial espionage, or (c) maybe there were some other factors in the study that we haven't been told about, e.g., the rats were also being fed a strange chemical at the same time."

The fact that these reports have been available for so long without widespread scrutiny raises questions for Warwick. "One thing I am not clear about is how long these purported results have been known," he said. "The study mentions 1996 -- if the results have been known since that time, then Dow Chemical and the practitioners in the study are highly irresponsible individuals to have waited till now to say something."

A spokesperson for The Dow Chemical Company wasn't immediately available.

The AP report suggests that the Food & Drug Administration's approval of RFID implants may have been swayed by lobbying efforts rather than purely scientific considerations.

"The FDA is overseen by the Department of Health and Human Services, which, at the time of VeriChip's approval, was headed by Tommy Thompson," the AP report states. "Two weeks after the device's approval took effect on Jan. 10, 2005, Thompson left his Cabinet post, and within five months was a board member of VeriChip Corp. and Applied Digital Solutions. He was compensated in cash and stock options."

Thompson denied influencing the FDA's approval of VeriChip's technology. "I had nothing to do with it," he told the AP. "And if you look back at my record, you will find that there has never been any improprieties whatsoever."

The FDA stands by its approval processes, according to the AP.

Warwick said that he has no financial involvement with any RFID vendor. "I have no interest in or with any RFID company of any type -- my experience has always been purely investigative/scientific," he said. "The answer I have given is therefore purely scientific -- no industrial/company/financial interest has swayed me one way or another."