Lymphoplasmacytic

Lymphoplasmacytic is an histopathologic term used to describe cells that show features of both lymphocytes and plasma cells. It is applied to characterize certain B-cell neoplasms as well as some reactive conditions in which the infiltrating population ranges from small lymphocytes to plasmacytoid cells with abundant cytoplasm and eccentrically placed nuclei. The term emphasizes a spectrum of differentiation between lymphoid and plasmacytic lineages observed in tissue sections or bone marrow.

Morphology: In tissue, lymphoplasmacytic infiltrates comprise small mature lymphocytes, plasmacytoid lymphocytes, and mature plasma cells. The pattern may be diffuse or interstitial, with varying degrees of plasmacytic differentiation. In bone marrow, the spectrum can range from predominantly lymphocytic to plasmacytic-predominant infiltrates, and plasmacytic components may express plasma cell markers on immunohistochemistry.

Clinical significance: Lymphoplasmacytic differentiation is most prominently associated with lymphoplasmacytic lymphoma (LPL), a B-cell non-Hodgkin lymphoma. LPL commonly involves bone marrow and lymphoid tissues and is frequently accompanied by an IgM monoclonal gammopathy, a condition known as Waldenström’s macroglobulinemia.

Immunophenotype and genetics: LPL cells often express B-cell markers such as CD19, CD20, and CD79a, and may show surface immunoglobulin. Plasmacytic components express plasma cell markers (e.g., CD138). They are typically negative for CD5 and CD23. A recurrent MYD88 L265P mutation is detected in many cases, and CXCR4 mutations occur in a subset.

Diagnosis and differential: Diagnosis relies on histology with immunophenotyping and molecular studies, distinguishing lymphoplasmacytic infiltrates from reactive plasmacytosis or other marrow disorders such as multiple myeloma or marginal zone lymphoma. Clinically, the association with IgM gammopathy helps differentiate Waldenström’s macroglobulinemia from other plasma cell disorders.