Microchips and Cancer

Photo Credit: Forrest Croce.

Photo Credit: Forrest Croce.

Recently, microchips for pets became mandatory in England and Scotland. This has resurrected some of the media misinformation that has long gone around on the internet about the “dangers” of microchips, particularly the potential for cancer.

Here is what you need to know about the risks, and how to reduce or eliminate them:

  • There is tremendous variation in strains of rodents used in microchip studies; many were strains bred to be especially susceptible to tumor formation; unsurprisingly, they formed tumors at a rate many times higher than other strains. The fact that these genetic outliers develop so many tumors is not directly applicable to cats or dogs.
  • Any injection, bruise, wound, or other trauma has the potential to cause cancer (fibrosarcoma) in any animal due to inflammation, but cats seem to have an extreme susceptibility. In one unusual case, a surgical staple initiated a cancerous growth [Canadian Veterinary Journal. 2013 April; 54(4): 377–380.]; in another, non-absorbable suture material was to blame [Veterinary Journal, vol. 163, no. 1, pp. 105–107, 2002].
  • Killed vaccines (rabies, feline leukemia, and FIV) are, by far, the most commonly implicated tumor-causing agents because they are designed to create inflammation in the area of injection.
  • With cats, ANY injection or trauma may cause cancer, including subcutaneous fluids–a procedure used on tens of thousands of cats every day. But we don’t stop giving fluids because the needle might cause cancer. The risk is small, and a risk-benefit analysis is, in most cases, quite clearly in favor of the chip.
  • At least 10 million dogs, cats and horses have been microchipped, yet Dr. Barb Powers, the renowned and much-awarded pathologist at my alma mater, Colorado State University, said she had seen only one case of microchip-associated cancer in her entire career. CSU receives samples not just from its veterinary teaching hospital, but all over the entire western region, and was the first lab to discover and describe vaccine-injection sarcomas in the 1990s.
  • The chances of even a strictly indoor cat getting out, lost, or stolen are much, much higher than the chances of a tumor resulting from a microchip. Having a microchip makes it much more likely you will be reunited with your cat.
  • My cats are indoors only (except for leash excursions), yet over their lifetimes (14 and 17 years so far) they have each slipped out at least twice. Fortunately, I’ve found them quickly with no harm done. But ALL my animals are and always will be microchipped; in my opinion, it’s cheap “insurance.”
  • According to research by the ASPCA, of all cats entering shelters, approximately 37% are adopted, 41% are euthanized, and less than 5% of cats who came in as strays are returned to their owners.
  • Another study found that registered owners were found for 74% of dogs and 63.5% of cats. The median return-to-owner rates for the shelters were 2.4 times higher for dogs with a microchip than all stray dogs (52.2% vs. 21.9%) and 21.4 times higher for cats with a microchip than all stray cats (38.5% vs. 1.8%). [Journal of the American Veterinary Medical Association. 2009 Jul 15;235(2):160-7.]
  • It’s true that microchips are not 100% reliable (they can migrate, break, malfunction, or fail to read on some scanners), but these comprise less than 1% of all chips. [International Scholarly Research Network, ISRN Veterinary Science Vol 2011, Article ID 210982] The stories of chipped pets being returned home are now so numerous that only the really remarkable ones (e.g., a pet found 7 years and thousands of miles away) are considered newsworthy.
  • My own cat was one of the rare reacters: within 24 hours, he produced a spectacular sterile abscess that covered his whole shoulder and ram halfway down his leg; it resolved in a few days. Fortunately he did not go on to develop cancer, even though he was a prime candidate with a genetically weak immune system.
  • To ensure the best results with minimal risk, I recommend that the chip should be placed slightly off the midline and away from all acupuncture meridians (particularly the bladder meridian, which runs parallel to but a small distance away from the spine). A dose of homeopathic Ledum 30C should be given immediately afterward. Extra supplementation with antioxidants for a few weeks will  reduce the oxidative stress and inflammation from which these tumors arise.
  • You should monitor the inflammatory reaction at any injection site, whether vaccine, microchip, slow-release drug, or any other jab. A small granuloma will (and should) appear at the site; but it should resolve within a month. Research has shown that If it does not shrink, or if it continues to grow, past that period, then the chance of tumor formation goes way up. It may be wise to consider having the granuloma (and chip) surgically removed with good margins. This will prevent the chronic inflammatory process that is most likely to convert to cancer. This will separate out and protect the rare hyper-reacters from the vast majority of pets who never have any adverse effects.
  • If you do microchip, be sure to keep the database up to date with your current contact information. Every time I move, one of the first things I do is contact AKC and update my pets’ info. A microchip will do no good at all if the finder cannot find you!
  • I do *not* agree that microchipping should be mandatory. That seems to me a vast overstepping of governmental authority. It’s a case of “Pay your dime and take your chances.” Those who choose to avoid the risk should have a right to do so.



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2 comments for “Microchips and Cancer

  1. jhofve77
    June 17, 2011 at 8:09 am

    It is certainly up to the guardian to keep their info current in the microchip database! But even though one of my own cats developed a horrible abscess from a chip, I still microchip all my animals. The technology isn’t perfect, but to me it’s added insurance in case my indoor cats get out…in fact just the other day Sundance waltzed right out the back door as I was taking out the trash. Of course collars and tags are needed, but they can come off, and I’ve seen cats get their jaw or a foot stuck in the collar, not to mention collars catching on fences or trees and potentially hanging the cat. Cats should have breakaway collars, but of course those collars are easily lost. Guardians have to balance the handful of documented cases where the chip has initiated cancer against the hundreds of lost pets who have been returned to their homes, thanks to chips. I don’t worry too much about the conspiracy theories about microchipping people, of course I’m probably past the age where that future will get me! But thank you for writing and expressing your concerns–people should understand both risks and benefits before making that decision!

  2. wk
    June 16, 2011 at 10:54 pm

    I have lost 5 pets to cancer in 4 years. All but one was microchipped. I HATE the chips. Working w/rescues many chips were not registered to the correct owner. Many chips migrate. RFID companies are making a fortune pushing chips. Next will be kids and people. Not everything is as great as it appears to be. Get a good collar and tags on your pets. Best thing is not to let them out! www (dot) ChipMeNot (dot) org
    www (dot) ChipMeNot (dot)org (dot)uk



    Just like vets seem to believe CONVENIA (long acting antibiotic) is so great…it almost killed my small dog & $1400 later she made it after week in intensive care. That shot is killing a lot of cats especially.

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