<aside> 💡 CD19+, CD20+, CD25+, CD27+, sIgM+; CD5, CD10, CD23 can be expressed in 10-20% cases.

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• More common in European descents and 20% of WM patients are of Ashkenazi Jewish ethnic background. Familial disease has been reported commonly, including multigenerational clustering of WM and other B-cell lymphoproliferative diseases.
  • Familial clustering of WM with other immunologic disorders, including hypogammaglobulinemia and hypergammaglobulinemia (particularly polyclonal IgM), autoantibody production (particularly to the thyroid), and manifestation of hyperactive B cells, has also been reported in relatives without WM.
• Incidence increases with age.
• The light chain of the monoclonal IgM is κ in 75% to 80% of patients.

Diganosis

• Express pan–B-cell markers CD19, CD20 (including FMC7), CD22, and CD79. CD25+, CD138+, CD103-.
  • CD25 and CD27 are characteristic of the WM clone.
  • Clonal cytotoxic T-cell population in PB.
• Difficult to differentiate from MZL.
• No recurrent translocations have been described in WM, which can help to distinguish IgM myeloma cases that often exhibit t(11;14) translocations from WM.
• Transformation to DLBCL.

WHO Criteria for LPL and WM

Lymphoplasmacytic lymphoma

• Neoplasm of small B lymphocytes, plasmacytoid lymphocytes, and plasma cells.
• Usually involving bone marrow and sometimes lymph nodes and spleen.
• Does not fulfill criteria of any other small B-cell lymphoid neoplasm that may also have plasmacytic differentiation.

Waldenström macroglobulinemia

• Lymphoplasmacytic lymphoma with bone marrow involvement and IgM monoclonal gammopathy of any concentration.

Proposed Criteria for the Diagnosis of Waldenström Macroglobulinemia

• IgM monoclonal gammopathy of any concentration.
• Bone marrow infiltration by small lymphocytes, plasmacytoid cells, and plasma cells.
• Diffuse, interstitial, or nodular pattern of bone marrow infiltration.