Reader Beth wrote yesterday:
Hey Dr. Dori, I read your post about the pup in your yard. I’m interested to know more about your take on microchipping. I’ve heard it can cause tumors but I’m not sure how founded on fact of a theory that is….. talk to me Doc!
Thank you for reading and for your excellent questions about whether microchips cause tumors and what I think of them. Cats are very special creatures (as I’m sure you already know) and their bodies are very sensitive. They sometimes develop tumors as a result of inflammation. Inflammation is an activation of the immune system, the part of your body that helps with healing and fighting off infections. Years ago veterinarians were seeing a problem with cats developing a yucky type of tumor called a fibrosarcoma at the site where some vaccines were given. ** In response to this, cat-specific vaccines were developed and now this problem is extremely rare. While vaccines were incriminated as being one of the biggest culprits, any potential source of inflammation (therefore any shot or even a microchip implantation or even internal suture material from when your pet was spayed or neutered) can potentially cause tumor formation.
However…This is VERY VERY rare. A veterinary oncologist (cancer specialist) that I trust at Cornell says that he has seen one case of a microchip causing one of these tumors in his entire career, and has only heard of it occurring one other time. This is someone who sees patients with tumors all day, every day. So in terms of risk a microchip has an extremely low probability of causing tumors or any problems (except occasionally they fall out on their own so have your veterinarian check for one periodically.) In general, if there is any risk of your pet escaping, I think that microchips are a great idea because I have seen them reunite owners with lost or injured pets many times!
** The simplified way a vaccine works is by activating the body’s immune cells and basically tricking them into making memory immune cells. If a real infection presents itself, the healing cells then are already developed and can go right to fighting off the infection. This activation of the immune system would lead to this type of tumor in a very rare but noticeable number of cats (~1:10,000) so improved vaccines were developed.