MS4A1 and monoclonal gammopathy: Diagnostic criteria for WM are IgM monoclonal gammopathy of any concentration, bone marrow infiltration by small lymphocytes showing plasmacytoid or plasma cell differentiation, intertrabecular pattern of bone marrow infiltration, and surface IgM+, CD5±, CD10−, CD19+, CD20+, CD22+, CD23−, CD25+, CD27+, FMC7+, CD103−, and CD138− immunophenotype [2].