Teratoma

**Semantic type:** Neoplastic Process

**Definition:** A non-seminomatous germ cell tumor characterized by the presence of various tissues which correspond to the different germinal layers (endoderm, mesoderm, and ectoderm). It occurs in the testis, ovary, and extragonadal sites including central nervous system, mediastinum, lung, and stomach. According to the level of differentiation of the tissues which comprise the tumor, teratomas are classified as benign (grade 0 or 1), immature (grade 2), and malignant (grade 3). Grade 0 teratomas contain only mature elements; grade 1 teratomas have a limited degree of immaturity; grade 2 teratomas have a more extensive degree of immaturity; grade 3 teratomas are composed exclusively of immature tissues. The prognosis depends on patient age, tumor size and grade, and stage.

**Synonyms:** - Teratoma, NOS - Teratoma, Not Otherwise Specified - teratoma