Teratomas.

Teratomas are embryonal tumors that normally arise from germ cells [3] and are typically benign. They are defined as being composed either of tissues that are foreign to the area in which they form, or of tissues that derive from all three of the germ layers [4]. Malignant teratomas are known as teratocarcinomas; these cancerous growths have played a pivotal role in the discovery of stem cells [5]. ?Teratoma? is Greek for ?monstrous tumor?; these tumors were so named because they sometimes contain hair, teeth, bone, neurons, and even eyes. Teratomas have been medical curiosities for centuries, though it wasn?t until the 1960s that significant research into mice teratomas elucidated not only what these strange growths were, but also how germinal cells should normally function.