A CAUTIONARY NOTE REGARDING THE APPLICATION OF KI-67 ANTIBODIES TO PARAFFIN-EMBEDDED BREAST CANCERS

Immunocytochemical studies examining the Ki-67 proliferation marker in paraffin-embedded material have recently been made possible by the av ailability of several antibodies, notably MIB-1, which are readily app licable to microwaved sections. Using breast cancer material, the pres ent study examines correlations shown by these new paraffin assays and also by PCNA (proliferating cell nuclear antigen), an existing marker of proliferation, with the established Ki-67 cryosection assay. Paraf fin sections were microwaved prior to incubation with Ki-67 or MIB-1 a ntibodies. Signal detection was carried out with a biotinylated second ary antibody, peroxidase-conjugated streptavidin, and DAB/H2O2 chromog en. The results suggest that caution is required when studying prolife ration in paraffin-embedded breast cancers by immunostaining using Ki- 67 antibodies. Nuclear staining in wax sections (Ki-Par, MIB-1, PCNA) greatly exceeded that in cryosections (Ki-Froz) and thus correlations were notably absent between Ki-Par or PCNA immunostaining and the rout ine Ki-Froz assay. Immunostaining with MIB-1 or PCNA may, however, be useful to assess proliferation if cut-offs are applied to eliminate we ak immunostaining associated with wax sections. Thus, an approximately linear relationship was seen between MIB-1/Ki-Froz, which was improve d if only moderately or moderately/strongly MIB-1-positive cells were scored. Similarly, a significant correlation was also revealed between PCNA/Ki-Froz if such a cut-off was applied.