Replicative Mcm2 protein as a novel proliferation marker in oligodendrogliomas and its relationship to Ki67 labelling index, histological grade and prognosis

The grading and prognostic assessment of oligodendrogliomas is severely con strained and there remains a need for improved diagnosis. Recently, we have identified the minichromosome maintenance (MCM) family of proteins as a no vel class of proliferation markers. Mcm2 is a protein which forms part of t he prereplicative complex. It is necessary for this complex to be assembled at origins of future DNA replication during the G1 phase to allow genome r eplication in the subsequent S phase. Our aim was to determine whether anal ysis of Mcm2 protein expression in oligodendrogliomas is of diagnostic valu e. Immunohistochemical staining for Mcm2 was performed on an archival serie s of 32 oligodendrogliomas. These tumours have been previously characterize d for Ki67, mitotic labelling index and outcome. Cells showing expression o f Mcm2 were quantified as a percentage to provide an Mcm2 labelling index. We have demonstrated a good correlation between Mcm2 and Ki67 labelling ind ices (r=0.76, P<0.01) but immunohistochemistry for Mcm2 consistently identi fied a higher proportion of cells. Mcm2 labelling index was higher in grade III than grade II tumours (P<0.001). Cases with a high Mcm2 labelling inde x showed a poorer prognosis than those with a low index (P=0.497) in univar iate analysis, but with wide variation in this small series. Demonstration of Mcm2 expression is of value to demonstrate the proliferative fraction of tumours and is likely to be of prognostic value. Its study in a larger ser ies is therefore warranted.