Lymphoplasmacytic lymphoma and Waldenström macroglobulinemia, a decade after the discovery of MYD88L265P.

There has been remarkable progress over the past 80 years since Jan Waldenstrom first described patients with a hyperviscosity syndrome related to IgM paraprotein in 1944. The definition of Waldenstrom macroglobulinemia (WM) has evolved from a clinical syndrome to a distinct clinicopathologic entity with characteristic morphology, immunophenotype and molecular features. The landmark discovery of MYD88 mutation among most WM cases in 2012 marked the dawning of an era of molecular genomic exploration that led to a paradigm shift in clinical practice. In the current World Health Organization (WHO) classification of hematologic neoplasms, WM is included in the category of lymphoplasmacytic lymphoma (LPL) of which WM represents over 90% of cases. LPL/WM is also better defined, resolving ambiguity in many cases that would have been classified as "low-grade B-cell lymphoma with plasmacytic differentiation" a decade before. Nevertheless, challenges still face pathologists because criteria for distinguishing LPL/WM from other types of low-grade B-cell lymphoma, particularly marginal zone lymphoma (MZL), remain imperfect. In this review, we highlight the current understanding of LPL and WM brought to light by new discoveries, which in turn are increasingly translated to improved diagnosis and personalized therapy. Key concepts in the diagnosis and their clinical implications are emphasized. Controversies and challenges are also discussed.