Pathogenesis of intracranial germ cell tumors reconsidered

Object. To determine the pathogenesis of intracranial germ cell tumors (GCTs), the author studied 153 cases of these tumors encountered through 1994, 62.7% of which showed monotypic histological patterns and 37.3% of which were shown to be mixed tumors. Methods. Six patients died soon after admission and underwent autopsy; the other patients underwent surgery followed by radio- and/or chemotherapy. One hundred thirty-four cases were followed through the end of 1997. All patients with a choriocarcinoma died within 1 year. Patients with a yolk sac tumor (endodermal sinus tumor) or an embryonal carcinoma also had poor outcomes. Patients with a mature teratoma had 5- and 10-year survival rates of 93% each. Patients with an immature teratoma had 5- and 10-year survival rates of 86% each, whereas patients who had a teratoma with malignant transformation had a 3-year survival rate of 50%. Patients with a germinoma had a 5-year survival rate of 96% and a 10-year survival rate of 93%. These results may bring into question the validity of the germ cell theory because germinoma, which should be the most undifferentiated tumor according to the theory, was the most benign and choriocarcinoma and yolk sac tumor (endodermal sinus tumor), which should be the most differentiated tumors, were the most malignant according to results obtained during the follow-up study. Conclusions. Germ cell tumors other than germinomas may not originate from one single type of cell (primordial germ cells). The embryonic cells of various stages of embryogenesis may perhaps be misplaced in the bilaminar embryonic disc at the time of the primitive streak formation, becoming involved in the stream of lateral mesoderm and carried to the neural plate area to become incorrectly enfolded into the brain at the time of neural tube formation. The author propounds the following hypothesis: tumors composed of cells resembling the cells that appear in the earlier stages of embryogenesis (ontogenesis) are more malignant than those composed of cells resembling the cells that appear in the later stages of embryogenesis.