Somatic-type malignancy in germ cell tumors

Somatic-type malignancies (STM) may occasionally develop in preexisting germ cell tumors (GCT). It is generally believed to result from transformation of teratomatous elements, although alternative mechanisms must exist, as not all STM develop in teratoma-containing GCT. The transformed histology includes sarcomas, carcinomas, primitive tumors, hematologic malignancies, and others. STM-GCT occurs across the spectrum of GCT, including type I, type II, type III, and type IV GCT, and in both gonadal and extragonadal sites. Derivation from the preexisting neoplastic germ cell has been supported by the presence of molecular signatures of GCT in the somatic component. The STM likely arises from the activation of oncogenes that normally play a role in the development of these tumors at their normal sites. Pathogenesis includes senescence of tissues in slow-growing, benign GCT or overgrowth of immature elements. The presence of STM renders worse outcome compared to conventional GCT without transformation. STM is generally resistant to chemotherapy targeted at GCT. Stage and feasibility of radical resection are the most important prognostic factors. The differential diagnosis of STM-GCT includes metastatic non-GCT-related malignancy, post-therapy changes, and other GCT elements.