Flow cytometric S-phase fraction measurement in breast carcinoma: Influence of software and histogram resolution.

Background: S-phase fraction (SPF) measurement by flow cytometry is a clinically useful prognostic factor in patients with breast carcinoma. Standardized SPF determination is essential. As part of a multicenter study, we evaluated the influence of the choice of software and histogram resolution (256, 512, or 1,024 channels) on SPF quantification. Methods: One hundred thirty-three DNA histograms were analyzed in three laboratories with Modfit 5.2, Modfit LT, and Multicycle ANT software. Strict rules for histogram interpretation and software management were applied. The following five options were compared: MF 5.2 1024, MF 5.2 256, MF LT 256, MC ANV 256, and MC AV 512. Results: In the DNA diploid and aneuploid groups, SPF distributions were not statistically different among the five options. Excellent quantitative correlations were obtained between pairs of options. When using tertiles as cutpoints for SPF classification, concordance rates ranged from 79.7% to 93.2% for DNA diploid samples and from 87.8% to 95.9% for DNA aneuploid samples, the best results being obtained with software working with a similar histogram resolution. Conclusions: Standardized use of commercially available software, including the choice of histogram resolution, provides comparable SPF results.