Teratoma pathophysiology

Pathology classification of individual teratomas
Teratomas commonly are classified using the Gonzalez-Crussi grading system: 0 or mature (benign); 1 or immature, probably benign; 2 or immature, possibly malignant (cancerous); and 3 or frankly malignant. See also cancer staging. Teratomas are also classified by their content: a solid teratoma contains only tissues (perhaps including more complex structures); a cystic teratoma contain only pockets of fluid or semi-fluid such as cerebrospinal fluid, sebum, or fat; a mixed teratoma contains both solid and cystic parts. Cystic teratomas usually are grade 0 and, conversely, grade 0 teratomas usually are cystic.

Grade 0, 1 and 2 pure teratomas have the potential to become malignant (grade 3), and malignant pure teratomas have the potential to metastasize. These rare forms of teratoma with malignant transformation may contain elements of somatic (non germ cell) malignancy such as leukemia, carcinoma or sarcoma. A teratoma may contain elements of other germ cell tumors, in which case it is not a pure teratoma but rather is a mixed germ cell tumor and is malignant. In infants and young children, these elements usually are endodermal sinus tumor, followed by choriocarcinoma. Finally, a teratoma can be pure and not malignant yet highly aggressive: this is exemplified by growing teratoma syndrome, in which chemotherapy eliminates the malignant elements of a mixed tumor, leaving pure teratoma which paradoxically begins to grow very rapidly.

"Benign" teratoma may prove to be malignant
A "benign" grade 0 (mature) teratoma nonetheless has a non-zero risk of malignancy. Recurrence with malignant endodermal sinus tumor has been reported in cases of formerly benign mature teratoma, even in fetiform teratoma and fetus in fetu. A grade 1 immature teratoma that appears to be benign (e.g., because AFP is not elevated) has a much higher risk of malignancy, and requires adequate follow-up.

Teratoma with malignant transformation
A teratoma with malignant transformation or TMT is a very rare form of teratoma that may contain elements of somatic (non germ cell) malignant tumors such as leukemia, carcinoma or sarcoma. Of 641 children with pure teratoma, 9 developed TMT : 5 carcinoma, 2 glioma, and 2 embryonal (here, these last are classified among germ cell tumors).

Extraspinal ependymoma
Extraspinal ependymoma, usually considered to be a glioma (a type of non-germ cell tumor), may be an unusual form of mature teratoma.