The following is some information I received from a pet site newsletter that I thought might be of interest.

"Are microchips dangerous? Do they cause cancer in cats? As the veterinarian, I´ll work to give you information and alternative opinions about controversial topics. Here is information about the controversy surrounding dog and cat microchips.

Microchipping is widely used and a very successful method for identifying cats and dogs. Recently, reports have been in the media about microchips that may cause cancer.

Microchips are FDA approved devices used for permanent identification of pets. They are more commonly placed in dogs than cats. Many cat owners keep their cats indoors only and do not feel the need for identification (As a side note - this is totally untrue. Cats that accidentally get out the door have the biggest need for identification as they have the lowest chance of being reunited with their owners).

The chip is small, compact and easily inserted under the skin. Lost pets are "scanned" and the chip identifies a number that can be subsequently traced back to the owner. Millions of pets have been microchipped and approximately 2,000 devices have been implanted in humans worldwide (with the goal of implanting 45 million people in the U.S) without significant problems being reported.

Studies about the effects of microchip implantation have been going on for about 6 years after implantation. Mild inflammation was noted in some animals but most was gone within 3 months after implantation. There have been some reported adverse reactions in mice and rat studies. Reports surfaced that the glass-encapsulated RFID transponders microchips caused malignant, fast-growing, lethal cancers in up to 1% to 10% of cases in rats and mice. In 2004, a dog was examined for a mass over his shoulder area. The mass was removed and was found to be a sarcoma. Attached to the mass was a microchip. The dog had no reoccurrence and is apparently well. In this case, according to the abstract published in Veterinary Pathology, it was difficult to establish which was the primary cause of the neoplastic growth, because the dog had received several rabies vaccines and the microchip was detected close to but not included in the mass. A concause could then be hypothesized.

The question is...Do microchips cause cancer in cats?
The answer is – we don´t really know. There has been one reported case that they suspect the microchip could have been a problem but the dog was also vaccinated for rabies and a definite cause could not be determined. Are there more cases that have not yet been diagnosed? I don´t know.

What should you do if your cat has a microchip?
++I´d recommend having your cat scanned during his routine exam at your veterinarian´s office. Chips are generally injected over the back but can migrate from over the back to the sides. By scanning the cat, you will be able to determine if the chip works and the general location of the chip. Then I´d recommend feeling that area (just as women do a self-breast exam) for the presence of a mass or problem on a regular basis. If you feel any sort of mass, see your veterinarian immediately.++

My Final Thoughts - Should you microchip your cat?
Absolutely Yes! microchips are the best way of permanent identification of pets. The chips are considered reliable and an effective way to identify lost pets. At this point in time, we believe that they likelihood of a pet being lost and possibly being euthanized because he cannot be identified is way higher than the chance of the pet developing a tumor.

Thanks marcatmm for the info is really useful and I agree with you pets should be microchipped.. we never know if someday something happens and your cat gets lost!! with microchip any vet office or shelter would know who the cat belongs!

Once we move out from my mother in law´s house we´re definitely going to microchip Desmond... I always had dogs and they were all microchipped and they never had a problem with it.

A tip for those who live in USA: the humane society microchip pets for really cheap (only $25.00) the first saturday of every month.

The society I foster cats for often receives cats that have only been tattooed, but the problem with a tattoo is that over time the numbers/letters are very hard to read - and occasionally impossible. I´m also a believer in microchipping. The advantages definitely outweigh the risks.

I just had Midge chipped last month when she had her annual checkup. She has no street smarts of any kind and would not be able to find her way home, ever. I don´t get caught up in all the drama about unproven CA scares.

There were two points in the article I noticed. One was that the chip can move from its original location so it´s important to scan all over the cat and not just the back of the neck. Also it´s important for the owner to palpate the chip from time to tme to see if there is any unsual swelling in the area, although the evidence for cancer forming around the chips is very miminal at this time..

Both my cats are micro-chipped, it´s something you should do as a responsible cat owner.

De-sexing
Micro-chipping
Locking them in at night etc

I had pipsqueak microchipped about a week ago and i was patting him earlier and could feel the microchip under his skin is this normal??

Both my cats are microchipped and so far so good. It has also not migrated too far. They are both "indoor" cats but just in case!

Hi Becca yes it is normal to be able to feel it, it should just feel like a grain of rice. All my cats are inddors but they are all microchipped and wear id tags on collars just in case as well.

Two of my cats are microchipped during their last check up. It´s useful, especially if they are going outside.

All four of my cats are microchipped - I am just waiting for the day they can have GPS added to the chip then hopefully we will never lose another cat again

I´ve not had my guys microchipped. I didn´t even know about it until recently when I began coming to this site. I don´t think my cats are in any danger of getting lost because they don´t go outside unless I take them out on a lead.

I can see why it might be useful, though. Especially when I move and get a house, I plan on letting them outside more. I´ll likely get it done then.

I will definetly have Midge scanned, the next time she is at the vet, to check for migration. That is a good idea. Midge is so chubby that I have not been able to feel her chip. And yes, she is still on her diet.
Have some fun everyday!!
M and M

Our vet always scans our cats at the annual booster/checkup I haven´t noticed anything unusual but its useful to be aware of it - thanks.