Background: ATP is catabolized to adenosine in the tumor microenvironment, leading to excess adenosine and immunosuppressive effects via immune checkpoint protein adenosine 2A receptor (A2AR). NIR178 is an oral A2AR antagonist that selectively binds and inhibits A2AR, reactivating T cell-mediated antitumor immune response. This Phase I/II study evaluated NIR178 in previously treated pts with advanced NSCLC (NCT02403193). Method: Pts (ECOG PS 0-1) had received 1 prior line of therapy; EGFR/ALK pts had failed prior TKI therapy. Objectives: primary e determine MTD of single-agent NIR178; secondary e efficacy endpoints, PK, and evaluation of PD-L1 expression. Result: At 13 Dec 2017 data cut-off, 24 pts had been treated: median age 68 yrs, 46% male; 79% received prior immunotherapy; 22/24 (92%) pts had discontinued (due to progression [n¼13], death [n¼2], AEs [n¼2] or other reasons [n¼5]) and 2/24 (8%) pts remained on treatment. Dose levels evaluated: 80 (n¼3), 160 (n¼3), 320 (n¼7), 480 (n¼6), 640 mg BID (n¼5). There was 1 DLT: Gr 3 nausea (640 mg). The most frequent (20%) any-Gr AEs regardless of causality were nausea (67%), fatigue (63%), dyspnea (46%), vomiting (33%), chest pain and other (29%), gastroesophageal reflux disease, anemia, diarrhea (all 25%), anorexia, back pain, generalized muscle weakness and cough (all 21%). Drug-related Gr 3 AEs were pneumonitis (8%) and nausea (4%); no Gr 4 AEs were reported. Potential immune-related any-Gr AEs were rash (8%), pneumonitis (8%), hypothyroidism, increased ALT/AST (all 4%). NIR178 systemic exposure (Cmax, AUC) increased more than proportionally with dose. Efficacy data for 17/24 treated pts demonstrated responses and SD across the dose range, including 1 confirmed CR (480 mg) and 1 PR (80 mg), both in immunotherapynaïve pts. Durable SD >44 wks with tumor shrinkage was observed in 2 ongoing immunotherapy-exposed pts. Disease control was seen in pts with both high and low baseline PD-L1 expression. Conclusion: NIR178 was well tolerated; AEs were manageable and there were no Gr 4 drug-related AEs. Immune-related AEs may indicate immune stimulation. Clinical benefit was observed in immunotherapy-exposed and -naïve pts irrespective of PD-L1 status.