Answer: C. Somatic malignancy arising in a teratoma

Histologic Description: Areas of the tumor show scattered glands and islands of atypical cartilage typical of a teratoma. There are also areas of rhabdomyoblasts with abundant eosinophilic cytoplasm that in this slide also does not form expansile nodules greater than a 4x field. The remaining tumor is a “blue-cell” tumor composed of sheets of cells and numerous tubules which occupies over a 4x field without intervening other teratomatous elements.

Discussion:
Although the atypia in the cartilage resembles a chondrosarcoma, the atypical cartilage is focal and not sheeting out over a 4x field and does not meet the criteria for a somatic malignancy arising in a teratoma. The presence of areas of epithelial or mesenchymal atypia does not affect prognosis which remains stage dependent. Similarly, the rhabdomyosarcoma would also not qualify as a somatic malignancy arising in a teratoma. These tubules composed of primitive small blue cells are typical of a primitive neuroectodermal tumor (PNET) occurring in the testis. As the PNET overgrows the surrounding teratoma to the extent that it occupies >4x field without intervening teratomatous elements, it qualifies for a somatic malignancy arising in a teratoma. More common somatic malignancies arising in teratomas are: primitive neuroectodermal tumor (PNET) and rhabdomyosarcoma. Less frequently arising in teratomas are carcinomas, Wilm tumor, neuroblastoma, and other sarcomas. 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. Typically, metastatic somatic malignancy does not respond to the same chemotherapy as with the same tumor not arising in a teratoma. The best chance for cure with a somatic malignancy in a teratoma is if possible complete surgical resection.