Abstract: Background and purpose: Lymphoplasmacytic lymphoma/Waldenström macroglobulinemia (LPL/WM) is a rare subtype of indolent B-cell lymphomas and often needs to be distinguished with other subtypes of small B-cell neoplasms. This study aimed to observe the clinicopathological characteristics of LPL/WM and the frequency of MYD88 mutation in this category of neoplasm. Methods: The clinical, histological and immunohistochemical features of 10 cases with LPL/WM were retrospectively studied, and the MYD88 L265P mutation status was analyzed by using a polymerase chain reaction (PCR) assay and direct sequencing. Results: All patients were male with a medium age of 61 years. Common clinical manifestations included fatigue and anaemia. All cases presented with monoclonal immunoglobulinemia and bone marrow involvement. Microscopy of the biopsied lymph node revealed a partially preserved architecture, frequently with a patent sinus, and the neoplastic cells comprised variable numbers of plasma cells, small lymphocytes and plasmacytoid lymphocytes. Bone marrow biopsy displayed the same changes. Immunohistochemically, the neoplastic cells of all cases were intensively positive for CD20 and showed restricted expression of the immunoglobulin light chain κ. Six cases were positive for CD23, and 2 expressed CD5 at low level. No CD10-positive cases were identified. The Ki-67 index ranged from 5% to 30%. In addition, reactive plasma cells with IgG4 expression were noted in 2 cases. All of the 10 LPL/WM cases carried MYD88 L265P mutation, whereas the cases with other subtypes of small B-cell neoplasms as the control demonstrated a negative result. Conclusion: LPL/WM is frequently associated with typical clinicopathological features, although occasional examples may demonstrate aberrant phenotypes. As a characteristic molecular genetic aberration of LPL/WM, the implication of detection for MYD88 L265P mutation may provide additional, reliable aids in the diagnosis and distinction of this unusual tumour.

Key words: Lymphoplasmacytic lymphoma, Waldenström macroglobulinemia, MYD88 mutation, Diagnosis, Differential diagnosis