Here are some other articles about this issue.
It sounds like the risk is pretty low, especially if you do not have a sarcoma prone breed (like golden retrievers.) For us, I think it is worth it, since our dog has such a high prey drive and runs so fast. If he gets away from us, there is not much chance we would be able to catch him. That is why we work so hard on recall, but if that fails, the microchip is the only chance we have of getting him back.