A simplified working formulation of non-Hodgkin's lymphomas based on quantifiable histologic criteria

Quantifiable criteria for a Simplified Working Formulation of non-Hodgkin's lymphomas are proposed. Biopsy specimens from 582 patients followed from 8.5 to 18.0 years were classified according to the Working Formulation. In addition, on hematoxylin and eosin-stained histologic sections, differential counts among six lymphoma cell types were performed. In each lymphoma 100 cells were counted from representative areas. The intralymphoma variation observed by this method was insignificant for the reproducibility of classification. Five histologic types were defined: (1) follicular small cell (less than or equal to 25% large cells), (2) follicular large cell (greater than 25% large cells), (3) diffuse small (less than or equal to 10% large cells), (4) diffuse large cell (greater than 10% large cells), and (5) lymphoblastic (greater than 20% lymphoblasts). These criteria had clinical significance with regard to prognosis, leukemic conversion, and meningeal involvement. The intraobserver and interobserver reproducibility of the Simplified Working Formulation was, respectively, 91% and 88%.