Chronic myeloproliferative disorders: prognostic importance of new working classification.

Variants of chronic myeloproliferative disorders (CMPD) were compared according to their clinical features and classified by bone marrow biopsy appearances. Subsequently, this classification was further evaluated using survival data and histological variables from iliac crest biopsy specimens of an additional 1391 patients, making a total of 2241 patients available for analysis of outcome. The patients were grouped again into three main classes: "typical"; "variant"; and "transformed". "Typical" comprised the "classic" groups. "Variant" included the less uniform myeloproliferative syndromes, distinguished also by more variable clinical features, a different prognosis, and a greater tendency to fibrotic and blastic transformation. "Transformed" defined the end stages of both "typical" and "variant" types. Ten subgroups were distinguished by different histology and prognosis. Particular prognostic importance was assigned to atypia and immaturity of haemopoiesis, predominance of individual haemopoietic cell line, number and anomalies of megakaryocytes and progressive fibrosis. It is suggested that the proposed subclassification would be helpful for studies of epidemiology and therapeutic trials by allowing more homogeneous groups to be recognised.