Lack of prognostic significance of DNA ploidy and S phase fraction in breast cancer

DNA Ploidy and S phase fraction (SPF) were measured in Stage I and II breast cancers from patients with at least 8 years of follow-up, to assess the prognostic significance of these data. Disaggregated sections of formalin-fixed, paraffin-embedded tumour were analysed by flow cytometry. SPF was calculated using a rectangular model of S phase, after subtraction of background debris using an exponential model. 64% of tumours were DNA aneuploid. The median SPF was 4.5% for DNA diploid, and 10.9% for DNA aneuploid tumours. There were small reductions in survival at 10 years for DNA aneuploid tumours, and for tumours with above median SPF, but these were not statistically significant. The relative hazard for DNA aneuploid tumours was 1.20 (95% CI 0.81-1.76), and for high SPF was 1.31 (95% CI 0.87-1.98). Neither factor was statistically correlated with survival in multivariate analysis. Technical and theoretical factors limit the accuracy and reproducibility of flow cytometric data, and may explain the lack of prognostic information given.