MYCN Amplification in Medulloblastoma

Abstract

Prominent neuronal differentiation and MYCN amplification occur only in a small percentage of medulloblastomas (primitive neuroectodermal tumor of the cerebellum). In this article, we describe two medulloblastomas that showed a striking degree of neuronal differentiation with islands of mature neurons associated with abundant neuropil. In these differentiated foci, there were no mitoses or atypia, and the histology was reminiscent of a malformative or hamartomatous lesion. Both tumors were assessed for MYCN amplification by the novel technique of differential polymerase chain reaction (PCR) and fluorescent in situ hybridization (FISH). In case 1, MYCN amplification was in the 10-fold range determined by differential PCR, while in case 2 the level of amplification was marked, with 20-30 copies compared with diploid controls. FISH analysis also confirmed the presence of MYCN amplification in both tumors. These two cases are of great interest, especially as they show MYCN amplification in medulloblastomas with marked degree of neuronal differentiation. Furthermore, in both cases, there was evidence of a slower and more indolent clinical course, suggesting a more favorable outcome in medulloblastoma with this degree of neuronal differentiation.

Key Words:

• Primitive neuroectodermal tumor
• Medulloblastoma
• brain neoplasm
• MYCN
• polymerase chain reaction
• fluorescent in situ hybridization