IMMUNOREACTIVITY TO MIB-1 IN BREAST-CANCER - METHODOLOGICAL ASSESSMENT AND COMPARISON WITH OTHER PROLIFERATION, INDEXES

The recent availability of the monoclonal antibody MIB-1 (which is abl e to detect the human nuclear cell prolife ration-associated antigen K i-67 even on formalin-fixed, paraffin-embedded sections, microwave-tre ated and routinely processed for immunohistochemistry) could open new avenues for validation of the clinical role of tumour cell proliferati on on large, consecutive and unselected series of human tumours. Howev er, the routine use of such a marker requires a methodological standar dization as well as the comparative assessment of some technical and b iological aspects. The MIB-1 index was determined in parallel samples from 50 consecutive invasive breast carcinomas processed with differen t fixatives for different times. The median values of MIB-1 indices fo llowing 2, 6 and 24 h of formalin fixation were similar (29.4%, 30.6% and 29.7%, respectively) and consistent with those reported in the lit erature; squared linear regression coefficients were 0.99. The median values of MIB-1 indices were markedly lower in Bouin-fixed, paraffin-e mbedded, and in frozen samples (20.0% and 19.8%, respectively), with a poor correlation coefficient with the values detected following forma lin fixation (R-2=0.456). Moderate and poor correlations were observed between Ki-67 index and MIB-1 detected on frozen (r(s), 0.78) or form alin-fixed, paraffin-embedded samples (r(s), 0.47) and a minimal conco rdance was observed between TLI and MIB-1 or Ki-67 (r(s), 0.25 and 0.2 2, respectively). Our results indicate interference of the fixative ty pe on immunoreactivity to MIB-1 and also suggest that Ki-67 and MIB-1 reacted with different epitopes of the same antigen.