Flow cytometric S-phase fraction as a complementary biological parameter for the cytological grading of non-Hodgkin's lymphoma

Abstract

Fine-needle aspiration cytology (FNAC) is a technique that can overcome tissue-sampling disaggregation problems related to DNA flow cytometry analysis. The aim of this study, with long-term follow-up (median, 72 mo), was to investigate the prognostic value of DNA ploidy and S-phase fraction (SPF) in patients with non-Hodgkin's lymphoma (NHL), and additionally, the relevance of SPF in the grading of NHLs, using FNAC. The series comprised 76 patients with NHL (32 indolent and 44 aggressive tumors, including 14 Burkitt lymphomas) and 30 patients with reactive lymph node enlargement used as a control group. DNA flow cytometry was performed on fresh samples obtained by FNAC. NHL grading was done according to the updated Kiel classification. The 5-yr overall survival of patients with NHL was determined using the Kaplan-Meier method. All samples of the control group and 81.6% of the NHLs showed a DNA diploid pattern. Fourteen cases (18.4%) were DNA aneuploid with bimodal distribution: slight hyperdiploidy and near-tetraploidy. Despite the higher incidence of aneuploidy in aggressive than in indolent tumors (22.7% vs. 12.5%), no correlation between DNA ploidy and NHL grading was observed. In contrast, SPF revealed a strong correlation with grading (P=0.0001). The mean SPF values varied from 6.5% in indolent NHLs, to 20.4% in aggressive not-otherwise-specified (NOS) NHLs, and to 35.3% in Burkitt lymphomas. Nearly all aggressive NHLs had an SPF >15%, while the vast majority of indolent NHLs showed an SPF <10%. The mean SPF value in the reactive node group was 6.6%. NHL grading significantly was correlated to survival (P=0.004) only if the Burkitt lymphomas, which showed the best prognosis, were analyzed as an independent group. There was a trend that did not reach statistical significance (P=0.072) for a worse clinical outcome of patients with aneuploid tumors. When mean SPF values were used as cutoff points to divide both indolent NHLs and aggressive NOS NHLs into two proliferative subgroups, no differences in relation to survival were found (P=0.763 and P=0.994, respectively). Also, no proliferative difference was verified between indolent NHLs and the reactive lymph node group (P=0.223). These results show that flow cytometric SPF is a valuable complementary parameter for grading NHLs on FNAC samples, but it appears to give no additional prognostic information on subset analyses.