Waldenström's Macroglobulinemia: An Exploration into the Pathology and Diagnosis of a Complex B-Cell Malignancy

After 77 years since the initial description, Waldenström macroglobulinemia (WM) remains as a bone marrow neoplastic disorder with lymphoplasmacytic differentiation oversecreting a monoclonal immunoglobulin M (IgM). However, many biological and genetic aspects of this entity have been unraveled and it is now easy to correctly diagnose patients with this illness. The diagnosis requires the presence of a monoclonal IgM component and bone marrow lymphoid infiltration must be demonstrated. In addition, other small B-cell lymphoid neoplasms with plasma cell differentiation must be discarded. Although the clinical picture is highly heterogeneous, the diagnosis is much easier today compared to the past, since now we can demonstrate the presence of somatic mutations, especially the L265P mutation in the MYD88 gene, highly characteristic of WM (>90% of the patients), followed by the WHIM-like mutations in the CXCR4 gene (~35%). The identification of these mutations is very important, because they can modulate the response to new treatments with Bruton's tyrosine kinase (BTK) inhibitors. Thus, the conventional prognostic factors that predict the outcome of these patients (anemia, thrombopenia, high M component, high B2M, and advanced age), must be complemented with the genetic evaluation of the patient, that can help us in the prediction of the risk of transformation from asymptomatic to symptomatic forms (Del6q) and/or from indolent forms of the disease to aggressive lymphomas (CD79b mutations).