Molecular studies suggest that anaplastic oligodendrogliomas (OIII) can be subdivided into clinically relevant subgroups. We analyzed a retrospective series of 40 consecutive OIII operated at our institution and compared them to 10 grade II oligodendrogliomas (OII). Chromosome 9p status was compared to Bcl1, Myc and p16 expression by immunohistochemistry, clinical and histological data, and to event free survival (EFS) and overall survival (OS).

Chromosome 9p deletion was observed in 55 % of OIII (22/40) but not in OII, and correlated with both OS and EFS. Bcl1 expression was significantly higher in OIII (45 % versus 14% for OII) and correlated with MIB-1 expression, vascular proliferation, tumour necrosis and a shorter EFS. Myc expression was correlated with histologic grade (27% in OII, 35% in OIII) and to a shorter EFS in chromosome 9p non-deleted OIII. p16 expression was not correlated with grade but revealed two distinct expression profiles according to chromosome 9p status. In 9p non-deleted oligodendrogliomas, p16 hyperexpression was correlated with shorter OS in both OII and OIII whereas absence of p16 expression was correlated with shorter OS and EFS in 9p deleted OIII.