QUALITY-CONTROL FOR EVALUATION OF THE S-PHASE FRACTION BY FLOW-CYTOMETRY - A MULTICENTRIC STUDY

Flow cytometric measurement of the S-phase fraction (FCM-S) may be cli nically useful in human cancers to identify high-risk patients. Howeve r, its clinical application requires a methodologic standardization, a high feasibility, and the reproducibility of results within the same and among different institutions. The interlaboratory quality control program for FCM-S determination (promoted by the Italian Society of Ba sic and Applied Cell Kinetics) was carried out on DMA diploid and aneu ploid cell lines and human breast cancers. FCM-S was quantified by usi ng four mathematical models characterized by different rationales and differences in the degree and shape of background subtraction function s. A satisfactory agreement in FCM-S values among different institutio ns was observed for cell lines. In human breast cancers, a high reprod ucibility of FCM-S estimates obtained by the different institutions wa s observed by using the same model. Conversely, different models gave different FCM-S estimates. Intermodel differences were more evident in aneuploid than in diploid tumors. These findings could explain the co ntrasting results on the prognostic role of FCM-S in clinically compar able series of breast cancers and should be considered in future effor ts to define the optimal and most reproducible mathematical approach t o quantify cells in the S-phase. (C) 1994 Wiley-Liss, Inc.