Extragonadal teratocarcinoma in chimeric mice

Chimeric mice often are created through the genetic manipulation of the mou se embryo in the process of developing animal models of disease. These mice have variable percentages of their somatic and germ cells derived from the donor embryonic stem cells and host blastocysts. In the development of mou se models deficient in the breast cancer susceptibility gene 2 (Brca2) or t he 70-kd heat shock protein (Hsp70-2), 3-4-week-old chimeras developed sing le or multiple masses composed of both well-differentiated and poorly diffe rentiated tissues derived from all three germ layers. These cases of extrag onadal teratocarcinoma, a rarely reported tumor, may be related to the gene tic predisposition of the 129/O1a mouse strain used to generate the embryon ic stem cells.