Robust Ki67 detection in human blood by flow cytometry for clinical studies.

Aim: Ki67 is a prognostic and/or predictive biomarker in patients with malignancies. Flow cytometry is a powerful technology for single-cell multiparameter analysis. Results: We developed and validated a multicolor quantitative flow cytometry assay for detection of intracellular Ki67 expression in various immune cell subsets from human blood. The assay was optimized and showed excellent precisions. Assessment of the sample stability indicated that percentage changes from the fresh sample for the reportable results of interest were within 20%, up to 72 h after blood collection in the Cyto-Chex (R) BCT tube. Conclusion: The validated assay is sufficiently robust to analyze clinical samples. Easy access to peripheral blood enables continuous monitoring of Ki67 expression in blood as a biomarker, for example, for immunotherapy studies.