The tumors that originate from the primordial germ cells amount to ca. 4% of all tumors in childhood. Most frequently, they appear before 3 or after 12 years of age. Two thirds are benign.
These tumors develop from the primordial germ cells (PGC) that can be detected in the epiblast following the formation of the primitive streak 6 and with an initial migration proceed extra-embryonically into the endoderm of the umbilical vesicle. From there they immigrate via the mesenterium into the genital ridge (future gonads).
This migration occurs between the 4th and 6th week 11-14.
A pathologic PGC migration can lead to an ectopic localization (sacro-coccygeal, retro-peritoneal, mediastinal, intracranial and epiphyseal regions).
The germ cell tumors are classified as follows:
- Embryonic tumors
- Extraembryonic tumors
This histological classification reflects the degree of differentiation that the cells have reached before they degenerate malignantly. This can happen to the cells at the following stages:
- In the germ cell stage (germinoma)
- In some stage of differentiation that has progressed further within the embryo (teratoma, embryonic carcinoma)
- In some stage of differentiation that has progressed further outside the embryo (tumors of the umbilical vesicle, choriocarcinoma)