Immunophenotypic Analysis of Waldenstrom’s Macroglobulinemia: A Study of 63 Cases.

The immunophenotypic characterization of Waldenstrom’s macroglobulinemia (WM) is still unclear, despite being an essential tool in the diagnosis of hematological malignancies. We retrospectively reviewed the immunophenotypic profile of 63 cases of WM showing monoclonal IgM in the serum and morphological lymphoplasmacytic bone marrow infiltration, and of 26 cases of other chronic B-cell lymphoproliferative disorders having monoclonal IgM in the serum (LPD-M), including marginal zone (n=16), mantle cell (n=8) and follicular (n=2) lymphomas. The median age at diagnosis was 64[46–92] years. Immunophenotypic analysis was performed by flow cytometry between January 1998 and July 2007, using four or six monoclonal antibody combinations. In WM and LPD-M groups, all patients showed a monoclonal tumoral B-cell population, detected and studied in blood (21 and 23 patients, respectively), blood and bone marrow (19 and 2 patients, respectively) or bone marrow samples (23 and 1 patient, respectively). Patients with a Matutes score > 3 were excluded. Neoplastic cells, in all cases, expressed a monoclonal immunoglobulin light chain (kappa for 70% WM and 73% LPD-M, lambda for 30% WM and 27% LPD-M). The intensity of expression of the monoclonal light chain was particularly heterogeneous in both groups: high, normal or low expression in 43%, 27% or 30% of WM, and in 52%, 33% or 15% of LPD-M, respectively. Pan-B antigens (CD20, CD19, CD79b) were positive for at least 97% of patients. The results obtained with other antigens in WM compared to LPD-M were: CD10 = 10 versus 7%, CD23 = 33 versus 56%, CD5 = 14 versus 26%, FMC7 = 76 versus 89%, CD38 = 56 versus 41%, CD25 = 86 versus 84%, CD43 = 12 versus 16%, and CD11c = 10 versus 36%. The intensity of expression of these antigens was heterogeneous in both groups. Among the antigens only tested in the WM group, CD1c and CD27 were positive for 70% of patients, IgM and IgD for 95% of patients, and CD103 as well as CD117 were negative in all cases. Considering all (blood and/or bone marrow) WM samples, plasma cells (CD38/CD138 positive cells) were found at low levels (less than 2.5% of B-cells) for 46% of WM. Comparing blood versus bone marrow WM samples, no differences were found for all previous antigens except the higher frequency of low counts of plasma cells in bone marrow (observed in 71% of WM) versus blood samples (28% of WM). Among the 10 WM patients tested for ZAP-70 expression, nine were negative and one showed a low intensity expression. In conclusion, our results show that the immunophenotypic analysis usually performed with standard antigens in WM overlaps with other B-cell lymphoproliferative disorders. Studies involving the expression of new antigens and/or other biological approaches are required to identify the WM among the B-cell malignancies and are ongoing in our group.