Alpha-internexin expression in medulloblastomas and atypical teratoid-rhabdoid tumors.

OBJECTIVE To determine whether medulloblastomas and atypical teratoid/rhabdoid tumors express alpha-internexin, an intermediate filament protein that is expressed in normal neurons undergoing maturation and differentiation. MATERIALS AND METHODS 28 medulloblastomas and 5 atypical teratoid/rhabdoid tumors were examined for the immunohistochemical expression of alpha-internexin, as well as the neuronal markers peripherin and synaptophysin, and glial fibrillary acidic protein. RESULTS Overall, 21 of 28 medulloblastomas (75%) expressed alpha-internexin. More specifically, alpha-internexin expression was observed in 6 of 10 (60%) classic medulloblastomas, 12 of 14 (86%) desmoplastic medulloblastomas, 2 of 3 (67%) nodular medulloblastomas, and in one medullomyoblastoma. Similarly, 4 of 5 (80%) atypical teratoid/rhabdoid tumors expressed alpha-internexin. The extent of staining for alpha-internexin tended to be less than that of synaptophysin for both medulloblastomas (75% vs 93%) and atypical teratoid/rhabdoid tumors (80% vs 100%). In contrast to alpha-internexin, peripherin was expressed in only 4 medulloblastomas and one atypical teratoid/rhabdoid tumor. CONCLUSIONS Alpha-internexin is expressed in the majority of medulloblastomas and atypical teratoid/rhabdoid tumors, indicating that these primitive tumors usually exhibit neuronal differentiation.