Peter S. Rabinovitch MD, Ph.D. University of Washington, Seattle, WA, USA.

Significant progress has been made in improving the accuracy of DNA content and cell cycle measurements from univariate DNA histogram data. Notable improvements have been in the areas of 1) modeling of debris, including that generated from paraffin extracted cell nuclei; 2) software compensation for the effects of cell aggregation; 3) objective estimates of reliability of S and G2 phase measurements. These improvements have resulted in greater accuracy of cell cycle measurements from DNA histograms and improved prognostic significance of these measurements in the clinical setting. These improvements have been recognized by the recommendations formulated by the DNA Cytometry Consensus Conference (Cytometry. 14: 486-491, 1993). The same conference, however, stressed that future improvements in cell cycle measurements would have to come from bivariate DNA analyses.

Bivariate analysis is a rapidly expanding area of DNA content measurement. Exciting examples of this growth are in the analysis of cyclin expression, cytokeratin labeling and apoptosis markers (e.g. TdT end labeling of apoptotic DNA fragments). The movement to bivariate data acquisition has not yet been accompanied by corresponding advances in methods of bivariate cell cycle analysis. Objective methods are needed for selecting positive vs. negative cell populations as a function of DNA content, and the distribution of debris and aggregates in bivariate data has not been studied. Although simple techniques to meet some of these needs may become available, ultimately methods of true two-dimensional cell cycle analysis are needed.