Table 3.

Key papers describing PD-L1 expression in pulmonary LCNEC.

Study	Number of patients	PD-L1 antibody test	PD-L1 Cutoff for positivity	PD-L1 Expression Tumor Cells (TC)	PD-L1 Expression in Stromal Lymphocytes “Immune Cells” (IC)	Other findings
Abdel Karim et al. (46)	LCNEC (n=24)	LCNEC tissue microarray (TMA) from US Biomax	3/5 cases with positive TCs had 1% or less tumor staining 5/10 cases with positive ICs expressed 2% or less positive cells.	5/24 (21%)	10/24 (42%)	No correlation between Ki-67 and stage of disease.
Arpin et al. (47)	LCNEC (n=68)	Anti-PD-L1 22C3 antibody (kit and automat Dako, Dako, Agilent, USA)	Positive TC % of TCs with membrane PD-L1 labeling with >1% Positive ICs = the % of the IC surface labeled, IC negative = <1%; IC1 = 1–5%; IC2 = 5–10%; and IC3 = >10%	7/68 (11%)	49/65 (75%) (with >1% expression)	20/65 IC with >10% PD-L1. Median overall survival was significantly shorter for metastatic LCNEC patients with TC +/IC- samples as compared to TC+/IC- samples.
	• 65 assessable for IC score• 68 assessable for TC score
Eichhorn et al. (48)	LCNEC (N=76)	Antibody Clone: SP263; Ventana Benchmark Ultra, Ventana Medical Systems, AZ 85755, USA	>1%	17/76 (22%)	28/76 (37%)	Patients with both positive TC and negative IC had significantly worse 5 year survival.
Guleria et al. (49)	LCNEC (N=11)	Antibody clone SP263, (VENTANA Medical Systems, Inc)	>1% positive tumor cells	4/11 (36%)	5/11 (45%)	Variable PD-L1 expression on literature review.
Hermans et al (45)	LCNEC (N=98)	Monoclonal rabbit anti-PD-L1 clone 28-8 DAKO Autostainer Link 48 system with the PD-L1 IHC 28-8 pharmDx kit (DAKO, Agilent, USA)	Tumor proportion score (TPS) defined as % of tumor cells with complete or partial membranous staining at any intensity. TPS ≥ 1% was considered as positive.	16/98 (16%)	N/A	CD8 expression also documented. CD8 expression in tumor and stroma correlated with PD-L1 expression and improved overall survival.
Inamura et al. (50)	LCNEC (n=41)	Anti‐PD‐L1 rabbit monoclonal antibody (clone: E1L3N; Cell Signaling Technology, Danvers, MA; diluted 1:50)	≥5% were categorized as “PD‐L1 positive”	11/41 (27%)	N/A	In combined assessment of 74 SCLC and 41 LCNEC PD-L1 expression was significantly associated with lower overall mortality.
Kasajima et al. (51)	LCNEC (N=58)	Mouse monoclonal antibody directed against PD-L1 (clone 22C3, dilution 1:30, Dako, Glostrup, Denmark)	≥1% was considered as PD-L1 positive	5/58 (9%)	25/58 (44%)	In combined assessment of 127 SCLC and 58 LCNEC samples, PD-L1 positivity in IC but not TC was associated with CD8+ infiltration, increased tumor associated inflammation, and improved overall survival.
Kim et al. (52)	LCNEC (N=72)	Human B7-H1/PD-L1 antibody (R&D Systems, Minneapolis, MN)	3 categories of PD-L1 positivity reported	(>1%) 12/72 (17%)	(>1%) 33/72 (46%)	IC infiltration and PD-L1 expression on IC was more strongly correlated in LCNEC as compared to SCLC.
			TC1/IC1 1%- 9%
			TC2/IC2 10%-49%
			TC3/IC3 50%+
Ohtaki al (53).	LCNEC (N=95)	Rabbit monoclonal antibodies against PD-L1 (Cell Signaling, E1L3NR, 1:200 dilution)	Tumors with score ≥ 1 were graded as PD-L1 positive	70/95 (74%)	N/A	Patients with PD-L1 positive TC had better but not significantly better recurrence free survival.
Tsuruoka et al. (54)	LCNEC (N=106)	Rabbit monoclonal antibody (E1L3N, 1:800, Cell Signaling Technology, Inc., Danvers, MA, USA)	Semi quantitative H-score method, score used by multiplying the percentage of tumor area by staining intensity. Score of 1 was used as cutoff.	11/106 (10.4%)	N/A	PD-L1 status was also assessed in SCLC and was 5.8% as compared to 10.4% in LCNEC.

PD-L1, Programmed death-ligand 1; SCNEC, Small cell neuroendocrine carcinoma; LCNEC, Large cell neuroendocrine carcinoma; N/A, not available.