EVALUATION OF KI-67 REACTIVITY IN NEUROBLASTOMA USING PARAFFIN-EMBEDDED TISSUE

Aims: To examine the pattern of reactivity of Ki-67 in neuroblastoma a nd correlate this with al clinical prognostic criteria and bl cell cyc le statistics (using flow cytometry). Methods: Four micron sections of paraffin embedded (PE) tissue from 55 patients (25 pre chemotherapy a nd 30 post) were placed on to aminosialinised slides, dewaxed and rehy drated. Slides were pretreated in a microwave oven, endogenous peroxid ase activity blocked using 3% hydrogen peroxide and Ki-67 reactivity i nvestigated using a a streptavidin/biotin/peroxidase technique. DNA pl oidy was also performed from an immediately adjacent section on the sa me block using a FACScan and Cellfit software. Results: Ki-67 reactivi ty was well defined and highly reproducible. Eighteen out of 30 post c hemotherapy samples were totally negative, despite evidence of prolife ration on flow cytometry and all subsequently died of disease. As inte rpretation post chemotherapy was therefore deemed unreliable, this gro up was excluded from analysis. Reactivity in pretreatment samples rang ed from 0% to 67%; staining was restricted to the nucleus with a disti nct pattern noted in the nucleolus. Ki-67 positivity was lower in aneu ploid compared with diploid tumours (mean 26% vs 36%, NS). Among diplo id tumours, a lower percentage positivity was noted in those patients with better clinical prognostic parameters. Correlation however betwee n Ki-67 and SG(2)M phases of cell cycle was poor (R(s) = 0.39, NS). Co nclusion: Assessment of proliferation in neuroblastoma by Ki-67 reacti vity in paraffin embedded tissue is reliable in pretreatment samples a nd can be incorporated into routine immunohistochemical evaluation. La rger multicentre studies are required to further evaluate Ki-67 reacti vity as a prognostic indicator.