Detection of L265P MYD-88 mutation in a series of clonal B-cell lymphocytosis of marginal zone origin (CBL-MZ).

Clonal B-cell lymphocytosis of marginal zone origin (CBL-MZ) is a recently described entity characterized by the presence of clonal B cells in the blood and/or bone marrow (BM) with morphologic and immunophenotypic features consistent with marginal zone derivation in otherwise healthy individuals. CBL-MZ is commonly associated with paraproteinemia, usually immunoglobulin M (IgM), raising diagnostic difficulties from Waldenstrom macroglobulinemia (WM). The aim of the present study was to determine the presence of MYD-88 L265P mutation in a well-characterized series of CBL-MZ to identify cases that may in fact represent WM. Fifty-three CBL-MZ cases were retrospectively evaluated. MYD-88 L265P mutation was determined by allele-specific polymerase chain reaction in blood and/or BM mononuclear cells. Almost half of the CBL-MZ cases (49%) were associated with paraproteinemia mainly of the IgM type (65%). MYD-88 L265P mutation was identified in 10 cases (19%). These cases may truly represent WM, whereas 43 cases (81%) are still classified as CBL-MZ. Mutated cases were all associated with paraproteinemia compared with 37% of the nonmutated ones (P < .0001). In addition, mutated cases displayed more frequently CD38 and CD25 positivity (P = .002 and P = .005, respectively). Moreover, cases without paraproteinemia presented more frequently with lymphocytosis, irrespective of the presence of the MYD-88 mutation (P = .02). The present study demonstrates that MYD-88 L265P mutation may represent the only sensitive marker for the differentiation of CBL-MZ from probable WM. However, further studies are warranted to better define the biological significance of MYD-88 L265P mutation and to clarify whether the presence of the mutation establishes WM diagnosis or that it can also be present in borderline cases associated with paraproteinemia.