In contrast to WM and IgM-MGUS (>90%) [12,13,14,15,46], MYD88L265P is absent or less frequent in other related B-cell (including IgM-secreting) disorders, such as mucosa-associated lymphoid tissue lymphoma, splenic marginal zone lymphoma, nodal marginal zone lymphoma, IgM-secreting multiple myeloma, and chronic lymphocytic leukemia, therefore representing a useful tool for discriminating WM from other related B-cell disorders at diagnosis (Table 1) [23,24,50,51,52,53,54,55,56]. This evidence concerns the gene CD40LG and splenic marginal zone lymphoma.