Immunohistochemical detection of phosphorylated STAT6 protein in specimens of PMBL, DLBCL, and cHL. (A) Staining for nuclear P-STAT6 was demonstrated in neoplastic cells of PMBL. (B) In nonmediastinal DLBCL, neoplastic cells were negative for P-STAT6 with only a few scattered reactive cells being positive. (C) HRS cells of cHL disclosed strong staining for P-STAT6. (D) Quantitative RT-PCR analysis of FIG1/IL4I1 gene expression in 4 DLBCL and 7 PMBL samples showing either positive (•) or negative (○) P-STAT6 immunostaining, original magnification, × 100.