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 nonHodgkin'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 (< 10 μm). A majority of the cells (an average of 45‐60%) in intermediate‐ and high‐grade lymphomas were in the range of 11‐15 μm. Only the intermediate‐grade large noncleaved and high‐grade immunoblastic lymphomas had a majority of their cells (> 50%) larger than 15 μm. 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 < 0.0001). Nearly two‐thirds of the cases in each grade were within specific ranges of mitotic indices, i.e., < 1 for low‐, 1‐3 for intermediate‐, and > 3 for high‐grade lymphomas.