The link between microchips and tumours in lab animals (rats and mice) has been known to exist for at least ten years. So I don't really understand the fuss about it now. I found two case reports in PubMed about dogs with microchip associated tumours and I have never personally seen one or heard from a colleague about one. So given the amount of microchipped dogs (cats, horses) in the last ten years I wouldn't worry too much.
Krisse (a vet) in Finland
