CD40LG and plasma cell neoplasm: These lesional cells demonstrated a kappa-restricted IgM immunophenotype (Fig. 5A, B, C, D, and E). These findings prompted the diagnosis of a clonal lymphoid lineage with plasmacytic differentiation with a differential diagnosis for B-cell lymphoma (i.e. lymphoplasmacytic differentiation vs marginal zone lymphoma) with an extreme level of plasmacytic differentiation and primary de novo IgM plasma cell neoplasm.