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We studied the clinicopathologic, immunophenotypic, and cytogenetic features of 26 patients with chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) associated with serum IgM paraprotein. The study group (16 men; 10 women; median age, 64 years; range, 40-82 years) represents approximately 2.5% of CLL/SLL cases at our institution. The paraprotein level ranged from 1 to 14 g/L (median, 4 g/L). Neoplasms in bone marrow were composed of small round lymphocytes arranged in nodular (n = 6), diffuse (n = 5), interstitial (n = 5), or mixed (n = 10) patterns. All cases were positive for monotypic surface immunoglobulin light chain, IgM/IgD, CD5, CD19, CD20, and CD23. CD11c (14/20 [70%]), CD79b (11/19 [58%]), FMC-7 (11/26 [42%]), CD22 (8/20 [40%]), and ZAP-70 (6/19 [32%]) were expressed in subsets of cases. Of 17 bone marrow specimens assessed by conventional cytogenetics, 6 were abnormal and 11 were diploid. The overall survival of this group (median follow-up, 24 months) was not significantly different from that for an age-, sex-and stage-matched group of 52 CLL/SLL patients without IgM paraprotein (P = .60). We conclude that CLL/SLL cases with serum IgM paraprotein are similar to other CLL/SLL cases in their clinicopathologic and immunophenotypic features.

We identified 382 consecutive patients with lymphoid neoplasms associated with serum monoclonal IgM paraprotein and classified each neoplasm according to World Health Organization criteria. Lymphoplasmacytic lymphoma/Waldenström macroglobulinemia (LPL/WM) was most common, 225 cases (median serum IgM level, 2.2 g/dL; range, 0.2-10.9 g/dL). For 157 cases, classification and median (and range in g/dL) IgM levels were as follows: chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL; n = 77), 0.9 (0.1-2.1); marginal zone lymphoma (n = 27), 0.5 (0.1-2.4); follicular lymphoma (n = 18), 0.4 (0.1-1.6); mantle cell lymphoma (n = 11), 0.4 (0.2-1.3); diffuse large B-cell lymphoma (DLBCL; n = 7), 0.5 (0.2-1.0); DLBCL associated with low-grade lymphoma (n = 5), 0.9 (0.4-3.0); angioimmunoblastic T-cell lymphoma (n = 4), 0.8 (0.8); and CD5+CD23- low-grade B-cell lymphoma, unclassified (n = 8), 0.5 (0.3-2.9). The results show IgM paraproteinemia was associated most commonly with LPL/WM (58.9%), followed by CLL/SLL (20.2%). Although serum IgM levels greater than 3 g/dL were restricted to patients with LPL/WM, most patients with LPL/WM had paraprotein levels less than 3 g/dL. Thus, serum IgM paraprotein level is not a reliable discriminator in differential diagnosis.