Primordial germ cells originate at the level of the yolk sac and migrate toward the posterior via the abdomen yolk channel and the mesentery then towards the gonadal ridges as early as the fifth week of gestation (Fig. 12.2). Aberrant migration is at the origin of extragonadic tumors.

GCTs are seen in 2–3 % of childhood cancers in western populations with a slight female predominance. The main locations are gonads and sacrococcygeal area (Table 12.1). Gonadal tumors are observed more frequently in adolescents, whereas extragonadal tumors usually occur in the newborn and infant. Extragonadal tumors are mostly arising from the sacrococcygeal area.

Patients with sex chromosome abnormalities are at higher risk of developing GCT. In Klinefelter syndrome (47, XXY), there is a high risk to develop extragonadal GCT. Mediastinal GCT associated with the Klinefelter syndrome is found in almost half of these patients. On the other hand, in the gonadal dysgenesis (45, X/46, XY) and in the case of ectopic testes, a high risk for developing a gonadal GCT exists.

GCTs may have various characteristics of benign or malignant behavior according to the histopathology, the site, and the age of the patient. These tumors may be undifferentiated or engage in ways of differentiation to the various tissues (Fig. 12.3). The pathological study should search for malignant components.

Teratomas contain at least a differentiation in two of the three embryonic layers (ectoderm, endoderm, and mesoderm). They can be mature or immature, and with or without malignant germ cells. In the mature forms, tissues are well differentiated, and the tumor may have organoid structures present (teeth, hair, bone, skin). Immature tissues contain suggestive elements of fetal or embryonic structures. Malignant characteristics may show endodermal sinus qualities, but also neuroblastoma, neuroepithelioma, and sometimes sarcoma characteristics, evoking a rhabdomyosarcoma or an angiosarcoma. Risk of recurrences or metastases is linked to the presence or not of the malignant component.

The germinomas also known as dysgerminoma , are the most frequent pure GCTs of the ovaries and the central nervous system. In the case of testicular origin, they are called seminoma. They are frequently found in patients with chromosomal aberrations or cryptorchidism. They may be difficult to distinguish from other round-cell tumors, and may also include choriocarcinoma foci.

Endodermal sinus tumors called also yolk sac tumors originate from totipotent germ cells, which differentiate into extraembryonic structures. These are the most common malignant GCTs in infants and are usually located in the testicles. During histopathological examination, they are identified by the Schiller-Duval bodies.

Embryonal carcinomas are aggressive histological forms and characterized by the presence of figures of anaplasia, frequent mitoses, and necrosis.

Choriocarcinomas have a histological aspects pattern to the placental chorion and consist of syncytiotrophoblasts or cytotrophoblasts.

GCTs have tumor markers. These tumor markers are of great importance for diagnosis, prognosis, and follow-up of. Those markers are alpha-fetoproteins (α-FP) and beta subunit of gonadotropin hormone (β-HCG) . These markers also called onco-fetoproteins are elevated in the serum but can also be highlighted by immunohistochemical staining of tumor tissue.

The α-FP is produced by embryonic liver, yolk sac, and at a lesser degree by the digestive tract. During the first months of life, this rate declines gradually to reach adult stage around the age of 1 year (<10 ng/dL) (Table 12.2).