Plasma cells in MCL tumors are SOX11 negative. (A) MCL with focal plasmacytic differentiation. Some cells show Dutcher bodies corresponding to the accumulation of restricted immunoglobulins (arrow) (H&E; ×60). (B-C) Tumor cells expressing restricted kappa light chain and BLIMP1 (×60). (D) Tumor cells expressing cyclin D1 (×60). (E) SOX11 expression is negative in the tumor cells but positive in internal controls such as endothelial and histiocytic cells (×60). Arrows point to tumor cells with Dutcher bodies.