Here's a great study:
Introduction
Implantable microchips have become a well-accepted means of pet identification
in the global veterinary community. Over the last 15 years, millions of dogs and cats
throughout the world have safely received an implantable microchip that can quickly and
reliably document the identity of a pet. As a result of this life-saving technology, some
8,000 dogs and cats are successfully reunited with their owners every month.
While the ability of microchips to drastically improve pet safety is unarguable, a recent
veterinary case report associated microchip implantation with sarcoma development
in 1 dog.1 Furthermore, in the context of microchip use in humans, sporadic reports
of sarcoma development in implanted laboratory mice and rats have received recent
publicity in the popular media.
Unquestionably, veterinarians would not continue to implant microchips if they believed
the devices presented significant, scientific risk of causing malignant tumors in dogs and
cats. However, because recent publicity has raised awareness and concern about this
topic, a review of the relevant database of research regarding both laboratory animals
and pets follows.
Conclusions
The use of microchips in pets is a safe, effective, and
durable means of identification that has been used
globally in millions of animals for nearly 2 decades.
To
date, the entire global database of sarcoma development
in microchipped dogs is limited to a single case report
involving 1 animal. Furthermore, though low incidences
of vaccine-related sarcoma development have been
documented in cats (even more rare in dogs), microchipassociated
sarcoma development has never been
reported in felines. In the context of millions of microchip
implantations spread over many years, this near absence
of adverse event documentation comprises an impressive
and expansive safety record. Therefore, the benefits of
microchip implantation with regard to the safety and
welfare of pets should they become lost or separated
from their owner have proven to be infinitely greater than
the remote and unsubstantiated risk of tumor development
associated with microchip implantation.
http://www.digitalangel.com/document...%2002%2007.pdf