Microchip Implants and Fibrosarcoma Formation

Filed Under: Dogs, Cats, General Care

Microchipping of pets has become an important tool reuniting pet owners with their lost and missing pets. A microchip is an electronic device approximately the size of a grain of rice that is implanted under the skin, usually in the shoulder area. The microchip itself is implanted through the use of a large bore syringe. The procedure is well tolerated by pets, allowing for permanent identification of the individual. When a pet becomes lost, a microchip reader at an animal control facility or veterinary clinic may be employed to obtain the pet ID number contained therein. Through their usage, the identification of the pet may be made even when a collar is no longer available or a collar has no permanent means of identification on it. It is estimated that in the U.S. 8,000 pets a month are reunited with their owners thanks to the use of microchips.

To date, many rescue groups, animal shelters, and veterinarians have touted the microchipping of pets as an important tool in the reuniting of pets and owners throughout the U.S. Some adoption groups have made there use mandatory in their quest to decrease the number of pets ending up in shelters.

In September of 2007, the Associated Press reported that the use of microchips in pets could lead to the development of a Fibrosarcoma. There was an unsubstantiated report of a single dog developing a fibrosarcoma following the use of a microchip. No direct link to the microchip was made other than geographical.

A research study has also linked the use of microchips with fibrosarcoma development. Unfortunately this study was conducted on a particular strain of mice predisposed to the formation of cancer. Veterinary oncologists presently believe this research to be flawed since the only strain of mice used to demonstrate a relationship between microchips and fibrosarcoma development was already predisposed to cancer formation. No additional reports or research has substantiated this proposed relationship.

A fibrosarcoma is a malignant tumor of fibroblasts that produce collagen in connective tissue. These tumors have been associated with irritation from vaccine adjuvants, injections of substances other than vaccines, such as corticosteroids, viruses, or even injury in an area. These tumors are locally invasive, often recur locally and have a tendency to spread (metastasize). These particular tumors are hard to control through surgery even when ancillary therapy such as chemo or radiation is employed in cats. In dogs, fibrosarcomas are typically a low-grade malignancy that commonly recur locally but will metastize infrequently. A correlation has been noted between canine fibrosarcoma development and injection site inflammation secondary to vaccination, but they are seen on a much less frequent basis in the dog as compared to the cat. The exact mechanism by which fibrosarcomas develop is presently unknown although certain individuals appears to be more susceptible to their development than others.

For now, the American Veterinary Medical Association or AVMA presently advises against a rush to judgment on microchip technology on the basis of one isolated case. The AVMA acknowledges that there is a need for more scientific research on the use of microchips. The AVMA also cautions against the removal of a microchip because it is an invasive surgery that may have possible complications of its own and any perceived risk from an implanted microchip is deemed to be extremely low at this time.


Tremayne, Jessica. “Chip Claim Gets under Oncologists’ Skin”. Veterinary Practice News. October 2007. Pp. 1 and 16.

“AVMA Weighs in on Microchip-Tumor Reports”. JAVMA Vol.231, No.8 News. October 15, 2007. p.1185.

Maxie, M. Grant Ed. Pathology of Domestic Animals. Vol. 1: 5th Edition. 2007. Saunders/Elsevier. Pp. 764-765.

Topics: microchip implants, tumors

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