Histological Description: In addition to the seminoma and yolk sac tumor, there is a nodule of primitive “small blue cell tumor” composed of sheets and tubules lined by malignant cells with high N/C ratio, numerous mitotic figures, and pleomorphism.

Discussion: This is an example of a Teratoma with Associated Non-Germ Cell Malignancy or synonymously a Teratoma with a Somatic Malignancy. The same histology can be focally seen within a teratoma, which has no significance and is not even mentioned in the report. A somatic malignancy is diagnosed when there are sheets of somatic elements not admixed with germ cell tumor occupying >4X power field. The most common somatic malignancies arising in teratomas are primitive neuroectodermal tumor (PNET) and rhabdomyosarcoma but any somatic sarcoma, carcinoma, or blastoma can be the somatic malignancy. These are seen in 3%-6% of germ cell tumors with a teratomatous component, and more frequent in metastatic sites following chemotherapy for a germ cell tumor. Non germ cell malignancies arising in teratomas retain chromosomal gains in 12p and typically do not show additional genetic alterations related to its somatic lineage (ie. PNETs arising in teratomas lack CD99 and lack t(11;22) seen in somatic PNETs, although they retain their synaptophysin positivity). Chemotherapy protocol specific to its somatic lineage is often used, although it is controversial whether it is superior to germ cell therapy. However, in the specific case of PNETs arising in teratomas, it has been shown that PNET therapy is better than germ cell chemotherapy. The best chance for cure is if the metastases are surgically resectable. Somatic malignancy in a teratoma does not alter the prognosis if confined to the testis. When a non germ cell malignancy arises in a metastatic teratoma the prognosis is markedly worsened with <50% patients achieving 3 year survival.