DIFFERENT CALCULATION METHODS FOR FLOW CYTOMETRIC S-PHASE FRACTION - PROGNOSTIC IMPLICATIONS IN BREAST-CANCER

S-phase fraction (SPF), estimated in the flow cytometric DNA histogram , is a prognostic factor in breast cancer. There are, however some inh erent difficulties in the estimation of SPF, such as the influence of debris, aggregates, and normal cells. Most of the available SPF calcul ation principles try to consider these difficulties, but so far no con sensus has been reached with regard to which principle is to be recomm ended. The aim of the present study was to investigate the prognostic impact of SPF when estimated with different calculation methods :Ln fr ozen breast cancer samples from 350 patients. Two nonparametric (R-man , R-min/both rectangle) and three parametric (ACAS/DNA-base, ModFit, a nd MultiCycle) calculation methods, with and without correction for de bris and aggregates, were used. The mean values for SPF varied from 4. 3% CACAS/DNA-base with correction for debris and aggregates) to 9.4% ( MultiCycle without any correction for background). The pairwise correl ation between methods varied considerably (R = 0.72-0.98). After categ orization of SPF values into low SPF (lower two tertiles) and high SPF (upper tertile), all methods yielded statistically significant Pvalue s for recurrence-free survival(median follow-up time 67 months), both univariately (0.0004<0.0001) and multivariately (0.048-0.0004), after adjusting for nodal status, tumor size, and estrogen receptor status. SPF with background correction did not yield lower P values than SPF w ithout. Regardless of which method was used, SPF showed similar correl ations with lymph node involvement, tumor size, and estrogen receptor content. in conclusion, as the mean value of SPF for different calcula tion methods varies, each laboratory must be restricted to use only on e method. Background correction does not seem to improve the prognosti c impact of SPF in DNA histograms. Based on the experiences obtained i n the present study, S-phase calculation methods without background co rrection may therefore be the most suitable for routine evaluation of DNA histograms of fresh frozen breast cancer material (ModFit, MultiCy cle, and R-man [the latter only for experienced operators]). The nonpa rametric R-min, with an automatic setting of the region used for SPF c alculation, may be an alternative, but suffers from the disadvantage o f not being commercially available yet. (C) 1998 Wiley-Liss,Inc.