How I diagnose B-cell lymphoproliferative disorders with plasmacytic differentiation

B-cell lymphomas with plasmacytic differentiation is a broad category that includes small and large B-cell lymphomas. In this review, we focus on the small B-cell lymphomas, which include lymphoplasmacytic lymphoma and marginal zone lymphomas, among others. We aimed to review the diagnostic criteria of each entity and the features that distinguish them from each other. We discuss the clinical presentation, morphology, immunophenotype, molecular features, and potential pitfalls of diagnosing B-cell lymphomas with plasmacytic differentiation and provide 2 illustrative cases. In some instances, small B-cell lymphomas with plasmacytic differentiation, particularly lymphoplasmacytic lymphoma and certain marginal zone lymphomas, have overlapping morphologic and immunophenotypic features. As a result, differentiating them may be difficult. In cases where classification is challenging, integration with clinical, radiologic, and laboratory findings may be helpful in arriving at a specific diagnosis. Instances remain, however, in which classification is difficult.