Expression of CD30 and OX40/CD134 in PTCL. (A) AIL. Biopsy shows a mixed lymphoid infiltrate with numerous thick-walled venules. CD30 immunostain is positive only in scattered plasma cells. OX40/CD134 stain shows clusters of positive cells with membrane and paranuclear staining corresponding predominantly to large tumor cells with clear cytoplasm. (B) Histiocyte-rich (Lennert’s) T-cell lymphoma. Predominantly small lymphocytes are intermixed with numerous epithelioid histiocytes. CD30 stain is negative; OX40/CD134 stain is positive in a majority of the small and large lymphocytes. (C) Angiocentric T-cell lymphoma. Lung with a predominantly large-cell infiltrate showing extensive infiltration of the wall of a large artery. OX40/CD134 staining is present in nearly all of the tumor cells. (D) ALCL. Colon biopsy shows a sheet-like mucosal infiltrate of anaplastic tumor cells (inset). CD30 stain is uniformly positive; OX40/CD134 stain marks occasional reactive T cells. Immunostain for ALK protein was strongly positive (not shown). (E) ALCL with a Hodgkin’s-like appearance. Tumor shows areas of strong CD30 staining and other distinct areas with strong OX40/CD134 reactivity.