Biological Heterogeneity of Diffuse Mixed Small and Large Cell Non-Hodgkin's Lymphomas Assessed by DNA Flow Cytometry and Ki67

Abstract

The cell proliferative activity of the clinico-pathologically heterogeneous non-Hodgkin's lymphomas (NHL) included in the intermediate grade F category of the Working Formulation (WF) was investigated. S-phase fraction with flow cytometry on cell suspensions, and Ki67 on frozen tissue sections were performed in 42 F NHL. An avidin-biotin irnmunocomplex method was used and 1000 cells from 10 representative fields were counted. DNA content, S-phase and Ki67 were also detected in 194 NHL covering the whole spectrum of the WF. DNA content anomalies were found in 52 of 194 NHL. Their incidence, like that of S-phase fraction and Ki67 positive cells, progressively increased from low- to high-grade. A linear correlation was found between Ki67 and S-phase (r =. 59). Using the median value of proliferating cells obtained with both procedures as a cut off, two very different groups of lymphomas could be distinguished within a series of 42 F-intermediate NHL: with low and high proliferative cell activity (p <.000l) that were termed F_low and F_high, respectively. A intermediate group was placed between them. It differed significantly from the others if Ki67 was used but only from the F_high, group if the S-phase fraction analysis was applied. No significant differences were seen when comparing F_low, with the single categories, of low-grade NHL and F_high, with H high-grade NHL; no significant differences were found between F_highand G, and between G and H categories. The existence of distinct groups of NHL in the F category, as defined by biological parameters assessing the cell proliferative activity, indicates that this category includes biologically heterogeneous lymphoma subtypes with different grades of aggressiveness. The results also indicate that the G intermediate category displays proliferation indices similar to those of H high grade category.

Key Words:

• F NHL
• biological heterogeneity
• DNA flow cytometry
• Ki67
• immunostaining