Expression of phosphorylated STAT3 in EBV⁺vs EBV⁻CHL. Nuclear pSTAT3 expression was detected with IHC. HRS tumor cells in both EBV⁺ and EBV⁻ specimens expressed pSTAT3 robustly at equivalent levels (P value not significant). (A) However, infiltrating lymphocytes in EBV⁻ specimens overexpressed pSTAT3, consistent with gene expression profiling results (P = .037, by a 1-sided Wilcoxon rank sum test). Horizontal black lines indicate the mean and the mean ± standard error of the mean. (B) Representative photomicrographs from EBV⁺ and EBV⁻ CHL specimens stained with anti-pSTAT3. Black arrows, HRS tumor cells; red arrows, lymphocytes. Slides were imaged at ×500 magnification with an aperture of 0.9. Bar, 20 μm.