Morphologic and molecular genetic aspects of oligodendroglial neoplasms1

Morphologic criteria for diagnosing oligoden-drogliomas and for classifying them as well-differenti-ated (World Health Organization grade II) and anaplas-tic (World Health Organization grade III) are well rec-ognized. Nevertheless, applying these guidelines to spe-cic cases often reveals discrepancies among different observers. In addition, whether a given tumor also con-tains an astrocytic component may be debatable. Loss of heterozygosity studies have demonstrated that oligo-dendroglial neoplasms have a high incidence of loss of the 1p and 19q chromosomal arms. Although loss of heterozygosity for portions of 19q are sometimes seen in astrocytic neoplasms, these tumors seldom show complete loss of 19q accompanied by loss of 1p. Loss of 9p or homozygous deletion of the CDKN2 gene or both are associated with anaplastic oligoden-drogliomas, whereas loss of 17p or TP53 gene muta-tions or both are frequent in astrocytomas, but rare in oligodendrogliomas. These observations suggest that molecular genetic parameters could provide an objec-tive, reproducible framework for classifying oligoden-droglial neoplasms. Neuro-Oncology 1, 52–60, 199