Clinicopathological characteristics of atypical teratoid/rhabdoid tumor.

The clinicopathological features of atypical teratoid/rhabdoid tumor, a new entity among malignant pediatric brain tumors, and the differential diagnosis from primitive neuroectodermal tumor (PNET)/medulloblastoma, and germ cell tumor are described. Histologically, atypical teratoid/rhabdoid tumor is defined as a polymorphous neoplasm often featuring rhabdoid, PNET, epithelial, and mesenchymal components. Atypical teratoid/rhabdoid tumors usually include PNET components and occur mainly in the posterior fossa, so mimic medulloblastoma. Atypical teratoid/rhabdoid tumor is characterized by the cytogenetic finding of monosomy 22 rather than i(17q). The tumor is similarly mistaken for PNET at supratentorial sites. Germ cell tumors also enter into the differential diagnosis due to their histological immunophenotypic diversity, particularly features indicative of epithelial and mesenchymal differentiation. Nonetheless, the remarkable spectrum of tissues that typify teratoma is absent in atypical teratoid/rhabdoid tumor. The same is true of germ cell marker in tumor tissues and serum. The prognosis of atypical teratoid/rhabdoid tumor is far less favorable than that of PNET/medulloblastoma of malignant or germ cell tumor. Meta-analysis of 133 cases, including 15 new and 118 reported cases, confirm that atypical teratoid/rhabdoid tumor is as a clinicopathological entity and emphasizes the necessity for distinguishing this unique tumor from other pediatric central nervous system neoplasms.