Working formulation of the non-Hodgkin's lymphomas: a study of cell size and mitotic indices in cytologic subtypes

Cell size and mitotic indices were studied in 243 non-Hodgkin's lymphomas (NHL) diagnosed cytologically and classified according to the Working Formulation. Low-, intermediate-, and high-grade lymphomas constituted 14.8%, 18.9%, and 61.7% of the cases, respectively. Measurement of the diameter of 100 lymphoid cells in each case showed that in most of the low-grade malignant lymphomas, 50-80% of the cells were small (less than 10 microns). A majority of the cells (an average of 45-60%) in intermediate- and high-grade lymphomas were in the range of 11-15 microns. Only the intermediate-grade large noncleaved and high-grade immunoblastic lymphomas had a majority of their cells (greater than 50%) larger than 15 microns. The mitotic indices (number of mitotic figures per 500 lymphoid cells) showed a highly significant difference between low- (0.7 +/- 1.14), intermediate- (3.0 +/- 2.67), and high-grade (5.4 +/- 3.40) lymphomas using the Wilcoxon's signed rank test (P less than 0.0001). Nearly two-thirds of the cases in each grade were within specific ranges of mitotic indices, i.e., less than 1 for low-, 1-3 for intermediate-, and greater than 3 for high-grade lymphomas.