PD-L1 expression is associated with ALK positivity and STAT3 activation, but not outcome in patients with systemic anaplastic large cell lymphoma

The programmed cell death 1 (PD-1) pathway is a recently recognized mechanism of tumor immune evasion. In this study, programmed cell death ligand 1 (PD-L1) expression was evaluated in 95 patients with systemic anaplastic large cell lymphoma: 45 ALK+ and 50 ALK−. ALK+ anaplastic large cell lymphoma was more often positive for PD-L1 than ALK− anaplastic large cell lymphoma (76% vs 42%, p = 0.002). ALK− anaplastic large cell lymphoma showed a strong correlation between PD-L1 expression and STAT3 activation (measured by pSTAT3^Tyr705) (r = 0.8, p < 0.0001). In contrast, the PD-L1/pSTAT3 correlation was weaker in ALK+ anaplastic large cell lymphoma (r = 0.4, p = 0.08). In ALK− anaplastic large cell lymphoma, the PD-L1+ subgroup was more often EMA positive (69% vs 20%, p = 0.02) and tended to be less often CD2+ (50% vs 83%, p = 0.059). In ALK+ anaplastic large cell lymphoma, PD-L1 was not associated with pathologic features (all p > 0.05). Negative ALK status and high IPI score (≥3) were associated with shorter overall survival (p = 0.009 and p = 0.0005, respectively). Overall survival was not different between patients with PD-L1+ vs PD-L1− anaplastic large cell lymphoma (p = 0.44), regardless of ALK status and International Prognostic Index (IPI) score. We conclude that PD-L1 expression is more common in ALK+ anaplastic large cell lymphoma than ALK− anaplastic large cell lymphoma. In ALK− anaplastic large cell lymphoma, PD-L1 is strongly correlated with STAT3 activation and is associated with more frequent EMA and less frequent CD2 expression. PD-L1 has no prognostic significance in predicting the outcome of patients with systemic anaplastic large cell lymphoma, regardless of ALK status. PD-L1 expression on the anaplastic large cell lymphoma cells suggests these patients as potential candidates for PD-1 blockade immunotherapy.