Apparently, there have been instances of this causing cancer (they also ran tests on mice) and has the potential of migrating from the original spot. To me, it's a personal choice and whether the risks (despite the slight chance) outweigh the benefits of recovering a lost dog. I won't judge the choice of the owner either way, since there are legitimate reasons of concern whether to do so or not. It can be the region, how active the dog is, how secure his environment is, etc can be taken into consideration also. It's always good to check that the scanner used in the surrounding areas is compatible with that particular microchip (which I've read can be a problem if the reader's different). I was going to microchip dahlia when I had her neutered, but decided against it after doing some research on this (and talking with a natural breeder). I still may do it and like I said, it *seems* like the percentage of risk is small right now like foods we eat that "can cause cancer". There has been so many rescue stories of dogs brought home because of their microchip but in my situation, the risk of cancer and dahlia getting lost/stolen seem to be comparable so I don't feel comfortable doing so until I know more information.
