Palmer et al., 1998: "Fibrosarcomas associated with passive integrated transponder implants." Toxicologic Pathology. 1998;26:170.
Summary: 800 mice were implanted with microchips for identification purposes as part of a larger study. After two years 2% of the mice had developed cancerous tumors (fibrosarcomas) around the implants.
Excerpt: "All tumors were observed. . .at or near the implantation site. . .[the tumors] were attached to the implant or partially or totally encased the implant."