Somatic Tumor-Like Neoplasms Arising With Testicular Germ Cell Tumors: Distilling Evolving Understanding, Terminology, and Implications for the Practicing Surgical Pathologist.

Tumors resembling conventional, somatic-type malignancies arise infrequently (<10%) in association with malignant, postpubertal-type testicular germ cell tumors, mainly at the metastatic sites (less frequently at primary), and often after treatment. Historically, the pathogenetic framework for these tumors, indeed their current classification and nomenclature under the WHO 5 th Edition, contemplated their arising from (malignant) postpubertal-type teratomatous components undergoing oncogenic changes homologous to conventional somatic malignancies of the relevant tissue lineages. Recent scholarship questions the specificity of their provenance to postpubertal-type teratoma, with strong evidence relating them also to postpubertal-type yolk sac tumor as well. In tandem, molecular studies support a close relationship to their associated postpubertal-type testicular germ cell tumor rather than identifying any of the known molecular drivers of the somatic-type malignancies they resemble. The histologic patterns observed include sarcoma-like tumors, carcinoma-like tumors, primitive-appearing embryonic-type neuroectodermal tumor, nephroblastoma-like tumors, neuroglial-like neoplasms, leukemia-like malignancies, and combined forms incorporating 2 or more of the foregoing. Although greater experience will be required to validate the changing conceptualization of their origin, from a management standpoint when seen at metastatic sites these somatic tumors-like neoplasms may be poorly responsive to cisplatin-based chemotherapy regimens whereas when seen in the primary site they behave favorably. Surgical resection, if feasible, may provide the best chance for sure at metastatic sites.