Comparison of monoclonal antibodies PC 10 and MIB 1 on microwave‐processed paraffin sections

Antibodies against the proliferation‐associated nuclear antigen (PCNA) and against the Ki‐67 protein are widely used as operational proliferation markers in human tumour diagnostics. The original Ki‐67 antibody had the inherent drawback in that it could only be used when fresh‐frozen material was available. The antibody PClO was supposed to offer the advantage that it could be applied on formalin‐fixed and paraffin‐embedded tissues. However, in cases in which the formalin fixation exceeded 4 h, PC10 staining proved to be inconsistent and often failed. The aim of this study was to compare a recently prepared Ki‐67 equivalent monoclonal antibody (MIB 1) and PC10 in routinely fixed histopathological material using antigen retrieval by microwave processing. Antibody MIB 1 stained the nuclei of cells known to belong to the proliferative compartments in microwave‐processing paraffin sections of formalin‐fixed tissues. Quiescent cells were consistently negative for MIB 1 staining. In contrast, PC10 was positive in almost all nuclei of different tissues in microwave‐treated paraffin sections. Thus, antigen retrieval by microwave processing is beneficial for the detection of the Ki‐67 protein in paraffin sections, whereas it is not needed for the detection of the PCNA.