NONSEMINOMATOUS GERM CELL TUMORS
Nonseminomatous histology comprises about 50% of all GCTs, and most frequently presents in the third decade of life. Most tumors are mixed, consisting of two or more cell types. Seminoma may be a component, but the definition of a pure seminoma excludes the presence of any nonseminomatous cell type. The presence of any nonseminomatous cell type (other than syncytiotrophoblasts) imparts the prognosis and management principles of a nonseminomatous tumor.
Embryonal carcinoma is the most undifferentiated somatic cell type. Individual cells are epithelioid in appearance and may be arranged in glandular or tubular nests and cords or as solid sheets of cells. Tumor necrosis and hemorrhage are frequently observed.
By definition, choriocarcinoma consists of both cytotrophoblasts and syncytiotrophoblasts. If cytotrophoblasts are not present, then the diagnosis of choriocarcinoma cannot be made. Pure choriocarcinoma is an extremely rare presentation usually associated with widespread hematogenous metastases and high levels of hCG. Hemorrhage into the primary tumor is frequent and is an occasional severe complication when it spontaneously occurs at a metastatic site. Elements of choriocarcinoma are frequently found in mixed tumors but appear to have no prognostic importance. Syncytiotrophoblastic giant cells can be seen as a component of any GCT (including pure seminoma). They impart no prognostic value by themselves.
Yolk Sac Tumor
Yolk sac tumor (endodermal sinus tumor) is often confused with a glandular form of embryonal carcinoma. This tumor mimics the yolk sac of the embryo and produces alpha-fetoprotein (AFP). The cells may have a papillary, glandular, microcystic, or solid appearance; and may be associated with Schiller-Duval bodies, which are perivascular arrangements of epithelial cells with an intervening extracellular space. Rarely, embryoid bodies resembling the early embryo can be seen. Yolk sac histology is rarely present as the only histologic subtype except in the mediastinum where pure yolk sac tumors account for a substantial minority of primary tumors. Pure yolk sac histology is the most common histology found in childhood GCT.
A teratoma is composed of somatic cell types derived from two or more germ layers (ectoderm, mesoderm, or endoderm). Mature teratoma consists of adult-type differentiated elements such as cartilage, glandular epithelium, nerve tissue, or other differentiated cell types. Immature teratoma generally refers to a tumor with partial somatic differentiation, similar to that seen in a fetus. Teratoma with malignant transformation refers to a form of teratoma in which one of its components, either immature or mature, develops aggressive growth and histologically resembles another malignancy. These usually take the form of sarcomas (most frequently embryonal rhabdomyosarcoma); and, less frequently, carcinomas (e.g., enteric-type adenocarcinoma), neuroectodermal tumors, or combinations of these. Acute nonlymphocytic leukemias have arisen in the context of mediastinal GCT, but not from other primary sites. Acute lymphocytic leukemia has been described. Although a mature teratoma may be histologically benign, it is derived from a totipotential, malignant precursor cell (embryonal carcinoma or yolk sac tumor). Therefore, a primary testicular tumor in a postpubertal male that displays only teratoma must be considered to be a fully malignant GCT, and management should proceed as if malignant components are present.