BACKGROUND: Waldenström macroglobulinemia (WM) is a subset of lymphoplasmacytic 
lymphoma (LPL) with bone marrow (BM) involvement and an IgM monoclonal 
gammopathy of any level. We aimed to identify the clinical, laboratory, and BM 
findings of patients with WM and to evaluate the usefulness of CD154 for the 
diagnosis and prognosis of WM.
METHODS: We reviewed the medical records and BM studies and/or flow cytometric 
immunotyping of 31 patients with untreated WM. Semiquantitative 
immunohistochemistry (CD20, CD138, tryptase, and CD154) of BM was performed.
RESULTS: Only six patients presented with symptoms of hyperviscosity syndrome. 
Eleven patients had solid cancer and/or another hematologic malignancy. Mast 
cells (MC) increased in all samples, with some in close contact with tumor 
cells. Tryptase-positive MC (17.1/ high-power fields [HPF], 1.2-72.0/HPF) and 
CD154-positive MC (8.6/HPF, 0.1-31.1/HPF) were observed. The high CD154-positive 
MC (≥8.6/HPF) group showed a lower overall five-year survival rate than the low 
CD154-positive MC (<8.6/HPF) group (71.9% vs. 100.0%; P=0.012). Flow cytometric 
immunophenotyping of BM aspirates showed increased B lymphocytes and plasma 
cells with a normal phenotype (CD138⁺/CD38⁺/CD19⁺/CD45⁺/CD56⁻).
CONCLUSIONS: Approximately one third of WM patients showed other malignancies 
and all patients had increased MC. Immunohistochemistry and flow cytometric 
immunophenotyping are useful for diagnosing WM, and increased CD154-positive MC 
can indicate poor prognosis.