Ultrarapid Ki-67 immunostaining in frozen section interpretation of gliomas

Background: Astrocytic tumours, the most common gliomas, are often classified intraoperatively using standard morphological staining. The final diagnosis and grading of gliomas on paraffin wax sections is often assisted by Ki-67 immunohistochemistry, but standard immunostaining protocols take too long to be used intraoperatively. Aims: To investigate a new rapid Ki-67 immunohistochemical test for its use in an intraoperative setting. Methods: The new Ki-67 immunostaining ( Ultrarapid-Ki67(R)) method on frozen sections can be carried out in 10 minutes. Thirty four pilocytic and diffuse astrocytomas were immunostained by rapid Ki-67 and results were compared with corresponding MIB-1 staining, histological grading, and prognosis. Results: The staining protocol was practical to perform and the results were morphologically and quantitatively indistinguishable from those after immunostaining with MIB-1, an antibody recognising Ki-67 in paraffin wax embedded tissue. A comparison of Ultrarapid-Ki67 and MIB-1 immunostaining of paraffin wax sections showed almost identical quantitative correlation in astrocytic gliomas ( r = 0.916; p< 0.001). The Ultrarapid-Ki67 indices ( percentage of positive cells) of low grade (I/II) astrocytomas ranged from 0% to 6.1%, whereas those of representative high grade (III/IV) tumours were significantly higher ( range, 5.6 - 45%; p< 0.001). The best prognostic cutoff point for Ultrarapid-Ki67 was 7.5%, which divided diffuse grade II - IV astrocytomas into significantly differing subsets ( p = 0.0008). Conclusion: Ultrarapid- Ki67 immunostaining is a useful adjunct to morphological diagnosis and grading of astrocytic tumours, and as a fast test (similar to 10 minutes for staining plus three to four minutes for scoring), it could be used in routine intraoperative diagnosis of gliomas and other neoplastic diseases.