QUALITY-CONTROL CONSIDERATIONS FOR KI-67 DETECTION AND QUANTITATION IN PARAFFIN-EMBEDDED TISSUE

Proliferative activity has prognostic significance in many solid tumor s. Immunohistochemical analysis of tumor proliferation may be accompli shed with the Ki-67 monoclonal antibody which recognizes a nuclear ant igen expressed throughout the cell cycle. This antibody, however, cann ot be used with formalin-fixed, paraffin-embedded tissue. Recently, a Ki-67 equivalent murine monoclonal antibody (MIB-1; AMAC, Inc., Westbr ook, ME) was generated which can detect tumor proliferative activity i n routinely processed tissue with microwave oven heating. Using quanti tative image analysis, we assessed the effect of delay in fixation, to tal time of formalin fixation, and microwave heating time on the immun oreactivity of this antibody. The effect of time to fixation (0, 2, 4, 8, or 24 hours) on MIB-1 immunostaining was determined in various tum or tissues using image analysis. No significant difference in positive nuclear area was observed for tissues in which fixation was delayed f or as long as 8 hours relative to controls. A 24-hour fixation delay r esulted in a small decrease in positive nuclear area relative to contr ols. The effect of fixation time (4, 24, or 48 hours) and microwave ov en heating time on MIB-1 immunostaining was studied in tonsil tissue, and quantitated by image analysis. Good MIB-1 immunostaining was obser ved for all microwave oven heating times in tissue fixed for 4 hours. In contrast, poor immunostaining was observed in tissue fixed for 48 h ours unless a heating time of at least 14 minutes was used. Tissue fix ed for 24 or 48 hours showed a significant increase in percentage posi tive area after microwave times of 14 or 21 minutes. Prolonged heating time (up to 49 minutes) had no effect on the quality of MIB-1 stainin g in tissue fixed for 4 or 48 hours. Ki-67 immunohistochemical stainin g is a simple and reliable method for studying tumor proliferative act ivity in formalin-fixed, paraffin-embedded tissue. The results of thes e experiments indicate that maximum recovery of Ki-67 immunoreactivity for analysis and quantitation is obtained in tissue fixed within 8 ho urs after removal and for as long as 24 hours, provided that a microwa ve heating time of at least 14 minutes is employed. The information ob tained on paraffin-embedded material by MIB-1 evaluation using image c ytometry may prove superior to S-phase fraction by flow cytometry, whi ch has been shown to suffer from various technical Limitations. (C) 19 94 Wiley-Liss, Inc.