Models of S-phase determination in lymphomas from flow cytometric DNA content histograms: Comparison with the bromodeoxyuridine labeling index

The estimated S-phase fraction (%S) of non-Hodgkin's lymphomas has been demonstrated to be of prognostic value. The %S can be determined by labeling index (LI) techniques or by various mathematical models applied to DNA content histograms. We performed DNA content analysis and a slide-based bromodeoxyuridine immunofluorescence LI on split samples from 117 biopsy specimens suspicious for lymphoma. The LI was compared with the %S determined by two computer models (rectangular and polynomial) with and without debris subtraction, and a manual gates computer model. In the 93 DNA diploid cases, the rectangular models had the highest correlation with the LI (R=0.88). In the 24 aneuploid cases, the manual gates model was the most useful because of a high correlation with the LI (R=0.70) and its ability to be used in most cases (23/24). The polynomial models had limited usefulness because they generally gave a higher %S than the LI and could be fitted in less than half of the DNA aneuploid histograms. These results suggest that in situations where the LI is not possible, an accurate %S estimate can usually be obtained with either a rectangular or manual gates model.