MS4A1 and lymphoplasmacytic lymphoma: Furthermore, many types of small B lymphoid neoplasms can display plasmacytic differentiation and a phenotype resembling lymphoplasmacytic lymphoma; the latter consists of small lymphocytes, plasmacytoid lymphocytes and plasma cells expressing IgM and pan-B-cell antigens, such as CD19, CD20 and CD22, and usually negative for CD5, CD10 and CD23.