Comparison of PD-L1 detection assays and corresponding significance in evaluation of diffuse large B-cell lymphoma

The expression of programmed cell death ligand 1 (PD-L1) is a biomarker for immunotherapy, but approved detection method is absent in diffuse large B-cell lymphoma (DLBCL). Here, we performed three methods including immunohistochemistry (IHC) (clone SP263 and SP142), RNAscope, and fluorescence in situ hybridization (FISH) to evaluate PD-L1 status on a cohort of DLBCL including 94 of DLBCL-NOS, 25 of primary mediastinal large B-cell lymphoma (PMBCL) and 7 of double-hit lymphoma (DHL). SP263 with 25% for immune cell (IC) or combined cell and SP142 with 10% for tumor cell (TC), 20% for both of IC and combined cell were proved to have corresponding survival prognostic. Combined⁺ showed comparable prognostic value with TC⁺ and IC⁺ . SP263 and SP142 showed strong concordance (k = 0.788) with combined⁺ rates of 33.3% (42/126) and 34.9% (44/126), respectively. In DLBCL-NOS, TC⁺ by SP263 preferred to non-GCB and immunoblastic variant DLBCL-NOS (P = 0.029 and P = 0.004). Combined⁺ (SP263 and SP142) were associated with more than one extranodal site involved (P = 0.006, P = 0.042), higher ECOG PS scores (P = 0.001, P < 0.001), high IPI risk (P = 0.012, P = 0.005), and poor treatment response (P = 0.095, P = 0.002). IC⁺ by SP263 and SP142 were both independent risk factors (P = 0.027, P = 0.037). 9p24.1 locus amplification and gain were identified in 4.3% and 7.6% DLBCL-NOS and indicated shorter overall survival (P = 0.004). Positive rate of PD-L1 by RNAscope was 36.5%, while no clinical significance shown. PD-L1 positive rates were all higher in PMBCL and DHL than in DLBCL-NOS by SP263, SP142, RNAscope, and FISH (P = 0.001, P < 0.001, P = 0.005 and P < 0.001, respectively). In conclusion, combined PD-L1 expression by IHC was potentially reliable and convenient as a predicting biomarker. SP263 staining was easier to evaluate and recognized more PD-L1-stained cells, but SP142 presented a better prognostic indicator. FISH and RNAscope could be used as supplementary assays. PMBCL itself was a sensitive cohort for immunotherapy.