Chapter 90

### Key Points

1. Fifty percent of pediatric germ cell tumors are extragonadal.

2. Teratomas (mature and immature) are the most common germ cell tumor and are benign lesions requiring only complete surgical resection.

3. Yolk sac (endodermal sins) is the predominant prepubertal malignant histology and alpha fetoprotein (AFP) is a marker of disease.

4. Accurate staging is essential as Stage I gonadal tumors are treated without chemotherapy.

5. The survival for malignant germ cell tumors treated with surgery and selective use of chemotherapy is excellent.

6. Current chemotherapy is extremely effective, thus resection of adjacent involved organs or structures is not indicated.

7. Initially unresectable extragonadal tumors treated with neoadjuvant chemotherapy and delayed resection have equivalent survival compared to initial resection.

Pediatric germ cell tumors are rare tumors with malignant germ cell tumors accounting for 1% to 3% of all malignant tumors in childhood. Several unique features distinguish these tumors: the nongonadal sites are more common than gonadal sites in children compared to adults where only 10% are extragonadal; yolk sac tumor is the most common malignant histology and alpha fetoprotein (AFP) serves as a marker to follow response to therapy and monitor recurrence; and, the introduction of modern chemotherapy with cisplatin, etoposide, and bleomycin has markedly improved survival and allowed the successful use of neoadjuvant therapy with preservation of vital organs.

Primordial germ cells arise near the allantois during the fourth fetal week and then migrate to the genital ridge where they develop into the gonads. Arrested migration is thought to result in the deposition of cells in extragonadal locations such as the retroperitoneum whereas aberrant migration results in the deposition at sites such as the pineal gland, mediastinum, and sacrococcygeal region.

### Classification

The totipotential nature of germ cells results in a wide variety of histologic patterns (Fig. 90-1). Seminoma or dysgerminoma, a primitive germ cell tumor is unusual in childhood occurring primarily in the adolescent years. Embryonal carcinoma is capable of further differentiation into embryonic and extraembryonic tumors. Teratomas are the most common germ cell tumors and are classified as mature or immature teratomas. Teratomas contain elements from 1 or more of the embryonic layers: ectoderm, endoderm, and mesoderm.

###### Figure 90-1

The developmental schema for germ cell tumors.

Mature teratomas contain well-differentiated tissues whereas immature teratomas contain neuroepithelium and are graded between 1 and 3 based on the number of low-power fields of primitive tissue. Although both mature and immature teratomas are considered benign lesions, accurate histologic evaluation is imperative as up to 25% of some malignancies are mixed tumors with more than one type of tissue. In addition, grade 3 immature teratomas are associated with microscopic foci of yolk sac tumor. Yolk sac tumor, a highly malignant tumor also known as endodermal sinus tumor is the most common malignant histology and occurs commonly ...

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