Expression of multiple B‐cell markers (CD19, CD20, CD22, CD79b), not bright CD38, and surface light chain restriction are features that support a diagnosis of DLBCL with marked plasmacytic differentiation, while lack of B‐cell markers and surface light chain expression and bright CD38 and diffuse CD138 favor a plasma cell neoplasm. The gene discussed is CD38; the disease is diffuse large B-cell lymphoma.