Embryonal neoplasm Teratoma 2009-02-03T05:23:03Z UMLS:C0039538 NCIT:C3403 Teratomas are germ-cell tumors commonly composed of multiple cell types derived from one or more of the three germ layers. They derive from embryonic pluripotent cells and may have various degrees of maturation, according to which they are classified as mature, immature, and malignant. Teratomas are found with decreasing frequency in the ovaries and testis, mediastinum, retroperitoneal space, sacrococcygeal zone, pineal and other intracranial locations. The presence of a teratoma. HP:0009792 SNOMEDCT_US:55818009 Germ cell neoplasia