An international, multi-institutional, clinical, pathologic study of 11 75 cases of non-Hodgkin's lymphoma sponsored by the National Cancer Institute has offered a unique opportunity to investigate issues of reproducibility and agreement in pathologic classification. Teams of experienced hematopathologists reviewed all 1175 cases, with the "experts" utilizing their own classification system and the experienced panelists utilizing all six of the histopathologic classification systems. The fact that 20% of the slides were randomly repeated for a second interpretation allowed assessment of the reproducibility of any one given pathologist. In addition, the agreement between and among pathologists was evaluated. Results of this retrospective study showed that both experts and panelists were able to identify follicular (nodular) or other indolent lymphomas with 95% probability of concurrence between initial and later interpretations. Moreover, individual pathologists agreed with others in identifying and classifying these follicular features with approximately 90% probability of agreement. The reproducibility for individual pathologists, based on the 20% of cases that were randomly repeated, varied from a probability 0.53 to 0.93. Comparisons of intersystem predictability demonstrated that no one system predicted for any of the other systems within any major degree of reliability. This inability to "translate" from one system to another is thought to be a reflection of the problems of both interpathologist agreement and intrapathologist reproducibility. Flaws in study design are discussed and the usage of the working formulation of non-Hodgkin's lymphomas, in addition to classification by traditional schemas, is strongly encouraged.
Cuncer 5591-95, 1985.
HE MULTIPLICITY of pathologic classification systems
T involved in the categorization of non-Hodgkin's lymphomas has resulted in both controversy and confusion. Over the last two decades there have been at least six major classification systems employed throughout the world. Because the terminology differs among them, it has been difficult, if not impossible, to compare clinical studies reporting diagnoses with differing classification systems, since there has been no equivalence of nomenclature in terms of prognosis. The classification of Rappaport].' has been the most commonly utilized in the United States; this system has undergone considerable revision as a consequence of the recognition of newer clinical pathologic entities, such as Burkitt's tumor and lymphoblastic lymphoma.
From the National Cancer Institute Non-Hodgkin's Classification Project Writing Committee.