Is a tumor which contains multiple types of tissue related to the three germinal layers i.e. ectoderm, mesoderm, endoderm, and are usually foreign to the part in which it arises.
Sites: the commonest site is the ovary. Types:
1- Benign teratoma: More common and may be:
b- Cystic (dermoid cyst): It contains hair, bone, cartilage etc..
2- Malignant teratoma: (rare) It usually shows a mixture
tissues one of which shows malignant change of
squamous cell carcinoma or adenocarcinoma, or may
contain immature tissues.
Origin of teratoma:
Many theories were put to explain the origin of teratoma. The most accepted one is that it arises from foci of totipotent embryonic cells which are capable of division into many types of cells related to the three germinal layers.