Subcutaneous soft tissue tumours at the site of implanted microchips in mice.

An experiment using 4279 CBA/J mice of two generations was carried out to investigate the influence of parental preconceptual exposure to X-ray radiation or to chemical carcinogens. Microchips were implanted subcutaneously in the dorsolateral back for unique identification of each animal. The animals were kept for lifespan under standard laboratory conditions. In 36 mice a circumscribed neoplasm occurred in the area of the implanted microchip. Females were significantly more frequently affected than male mice. An influence of age or different treatment on the s.c. tumour incidence in two mice generations could not be observed. Macroscopically, firm, pale white nodules up to 25 mm in diameter with the microchip in its center were found. Microscopically, soft tissue tumours such as fibrosarcoma and malignant fibrous histiocytoma were detected.