Immunohistochemical validation of paxillin and GRB2 expression in human malignant lymphomas. (A) Tissue microarrays composed of ALCLs (ALK positive and ALK negative) were used to perform immunohistochemical analyses for paxillin and GRB2. The morphologic features evaluated by H&E stains and expression of ALK-1, paxillin, and GRB2 in representative cases of NPM/ALK-positive ALCL, a variant ALK-positive ALCL (TPM3/ALK), and an NPM/ALK-negative nodal ALCL are shown. Paxillin and GRB2 are selectively overexpressed in the ALK-positive lymphoma cells in contrast to the ALK-negative nodal lymphoma cells. (B) The top panel demonstrates the features of a classical Hodgkin lymphoma with strong expression of CD30 in the neoplastic Reed-Sternberg cells that do not express ALK, paxillin, or GRB2. The bottom panel illustrates the morphologic features of a cutaneous ALCL with strong expression of CD30 but without expression of ALK-1, paxillin, or GRB2 within the neoplastic T cells.