Last week, the tragic story of Target the war dog hero  sparked a discussion among our readers about microchips and the possible risks. A couple of people asked about the research behind the risk claims, so I decided to explore the topic. This discussion is particularly timely because Merck was recently served with a lawsuit  over claims that its HomeAgain microchip caused cancer in a Massachusetts cat named Bulkin.
Unfortunately there are no large-scale, statistically valid experimental studies involving microchip implants in dogs, so we don’t know their long-term safety for sure. However, there have been a handful of studies with laboratory rodents, which is a start.
In six different studies with mice and rats, ranging from 1996 to 2006 , it was reported that 0.8 and 10.2 percent of the animals developed malignant tumors around or adjacent to implanted microchips. It’s a wide range, though the majority of studies had a 1-2 percent tumor rate. The studies also had a wide range of sample sizes, which may help account for the variation in findings.
Nonetheless, based on the rodent studies, it does seem like there is a small chance that microchips are linked to malignant tumors. Considering that millions of dogs have microchips, the fact we haven’t seen an epidemic of microchip-related cancer confirms that the percentage is probably very small.
However, as any dog lover knows, statistics mean nothing when your pet is the one affected. The cancer risk has been particularly interesting to me since I'll be adding a new puppy to the family soon and will have to make the microchip decision. Both of my current dogs are micrchipped and it's always given me peace of mind, particularly since they are not allowed to run at USDAA agility trials with their collars on. Knowing the possible risk, I will be sure to monitor the shoulder blade area (where my pups have their microchips) for any changes to the skin.
No form of identification is flawless and none of them is guaranteed to bring your pup home. It’s up to you to weigh the risks and the benefits and decide what is best for your pet.