Estimating the proliferative activity in breast cancer: Is Ki-67 immunostaining necessary?

The proliferative,activity (PA) of tumor cells has been shown to be a significant prognostic indicator in breast cancer. Ki-67 immunoreactivity in paraffin-embedded tissue has been shown to correlate with S-phase fraction as determined by flow cytometry. The aim of this work is to determine whether PA by Ki-67 immunostaining has significant advantage over mitotic figure count per ten high power fields (MF/1OHPF) or mitotic index (MI). Sections of formalin-fixed paraffin-embedded tissue of invasive breast cancer from 118 women were evaluated for MF/10HPF, MI, and immunostained for Ki-67 using the monoclonal antibody MIB-1. We found that PA determined by any of the three methods was a significant predictor of survival with p values of 0.016, 0.008, and 0.049 for PA determined by MI, MF/1OHPF, and Ki-67 respectively. We conclude that determining PA by KI-67 immunostaining does not have advantage over the traditional methods.