The role of cell cycle activity in the generation of morphologic heterogeneity in non-Hodgkin's lymphoma

Cellular and nuclear size heterogeneity are frequently observed in non-Hodgkin's lymphomas, yet the biological basis of this morphologic variability is not well understood. The possible relationship between cell size and cell cycle activity in malignant lymphomas was investigated using multiparameter flow cytometry and digital image analysis. Flow cytometric analysis of ten cases of B cell lymphoma revealed that, regardless of the diagnosis or the proportion of large cells present, large neoplastic cells showed a much greater proportion of S + G2/M phase activity (mean, 35.2%; range, 14.6% to 70.5%) than did small cells (mean, 4.4%; range, 0.5% to 18.4%). Further studies aimed at distinguishing the features of cycling and noncycling cells were performed using quantitative image analysis of nuclear staining by Ki-67 antibody. In both benign and malignant lymphoid infiltrates, resting (Ki-67-negative) nuclei were uniformly smaller than Ki-67positive nuclei and exhibited a restricted size distribution, whereas the Ki-67positive nuclei had a broad size distribution and included the vast majority of large forms. Thus, the actively cycling component of the tumor consisted of cells with large nuclei. These studies support the hypothesis that cellular and nuclear size heterogeneity in malignant lymphomas is related to cell cycle phase. The combined influences of cell differentiation and proliferation on cellular morphology can explain many of the histologic features observed in non-Hodgkin's lymphomas.