Tumor proliferative fraction in solid malignant neoplasms: A comparative study of Ki-67 immunostaining and flow cytometric determinations

Tumor proliferative fraction (TPF) has been shown to correlate with prognosis in some malignancies. A method for its determination that is practical, accurate, and reproducible is still being sought. In this comparative study of techniques, TPF values were determined in mirror-image samples of 126 consecutive solid malignant neoplasms using flow cytometry and immunostaining with Ki-67, a monoclonal antibody that recognizes an unknown nuclear antigen expressed during the entire cell proliferation cycle but not in resting cells. The mean TPF values for all cases were 19.5 ± 15.6% (percentage of tumor cells stained) by Ki-67 (range, 1-86%) and 15.7 ± 9.6% (S + G₂M) by flow cytometry (range, 3-60%), which correlated significantly at r = 0.53 and P = 0.005. The correlation was less strong in tumors with low S-phase values (≤10%, r = 0.28) than in tumors with intermediate and high S- phase values (r = 0.66). Ki-67 staining percentages did not correlate with patient age, sex, or tissue origin of the tumor. Ki-67 staining appears comparable to flow cytometry determination of TPF in solid malignancies with intermediate and high S-phase values. In tumors with low S-phase values, Ki- 67 immunostaining shows higher TPF values, which perhaps reflect an increase in the proportion of G₁-phase cells or dilutional effect of nonneoplastic cells in the tumors with low proliferative fraction.