Agreement rates and American-Japanese pathologists' comparability of a modified Working Formulation for non-Hodgkin's lymphomas. An analysis of the cases collected for the Fifth International Workshop on Chromosomes in Leukemia-Lymphoma.

Histopathologic slides of 368 cases collected from 16 institutions around the world for the Fifth International Chromosome Workshop were independently reviewed by a group of five hematopathologists consisting of two Americans and three Japanese. Agreement rates of their diagnoses using the Working Formulation (WF) for non-Hodgkin's lymphomas were studied. A modified classification scheme of the WF was used in order to define cytologic subtypes more specifically, enabling 65 possible diagnostic choices. Data analyses by computer revealed that at least four out of five diagnostic agreements were observed in 290 cases (78.9%). Similar agreements were observed in more than 80% of the cases for most of the categories of the WF, excepting diffuse small cleaved (73.3%), diffuse mixed (64.2%), diffuse large cell (76.5%), and immunoblastic lymphoma (70.2%). Agreement rates between American and Japanese pathologists did not demonstrate statistically significant differences against expected values. It was concluded that the WF was a reliable and useful classification system for multi-institutional as well as international projects, although refinements may be necessary in some categories for better diagnostic agreement.