Update on the WHO classification of myeloid neoplasms

Abstract

The 2001 WHO Classification of Myeloid Neoplasms was a major advance in the way myeloid malignancies are diagnosed, categorized, and communicated to treating physicians. A major tenet of the system is its reliance on a combination of morphology, immunophenotype, genetics, and relevant clinical information that together define biologically distinct disease entities. Our understanding of the pathogenesis of myeloid neoplasms has evolved rapidly in recent years, largely due to advances in molecular genetic technology and more complete characterization of genetic aberrations and gene expression patterns in various diseases; similarly, treatments have become more refined and increasingly incorporate therapies that target specific genetic lesions. The 2008 WHO Classification incorporated these advances by refining existing disease definitions and introducing new entities. This classification is currently being updated to reflect yet more recent data. In this Symposium, the background principles of bone marrow interpretation with respect to diagnosis of myeloid neoplasms will be reviewed, including accurate morphologic interpretation, use of flow cytometry and immunohistochemistry, and appropriate use of cytogenetics, FISH, and molecular genetic studies. Each category of myeloid neoplasms in the 2008 WHO Classification will be reviewed, with emphasis on recent advances and anticipated updates to the classification.