Background: The release of tumor-associated antigens may enhance the response to immunotherapy. BGB-A317, a humanized IgG4 variant monoclonal antibody engineered to have no Fc gamma receptor binding, targets the programmed cell death-1 (PD-1) receptor. It is being developed in solid and hematologic malignancies at a dose of 200 mg IV Q3W. BGB-290, a potent inhibitor of PARP 1/2, is hypothesized to promote neoantigen release that may potentially increase the efficacy of BGB-A317. A phase 1 study identified 60 mg BID as the recommended Phase 2 dose (RP2D) for BGB-290. This study consists of initial dose escalation to determine the maximum-tolerated dose (MTD), safety, pharmacokinetic (PK) profile, and preliminary antitumor activity of the combination, followed by expansion into ovarian, breast, prostate, gastric, bladder, pancreatic and small cell lung cancers. Methods: Cohorts of 6–12 patients with advanced solid tumors were treated in each of 5 planned dose levels (DLs). In DLs 1–3, BGB-290 doses ranged between 20–60 mg PO BID with BGB-A317 2 mg/kg IV Q3W. In DLs 4–5, BGB-290 doses were 40 or 60 mg BID; A317 was given at 200 mg IV Q3W based on PK data from a single agent Phase 1 study. Results: As of 31 March 2017, 43 patients [median age 63 years (34–75)] were treated in DLs 1–5. Three patients experienced four dose-limiting toxicities: grade 2 nausea (DL4), grade 2 nausea and grade 2 vomiting (DL5), and grade 4 autoimmune hepatitis (DL5). MTD was identified as BGB-A317 200 mg IV Q3W + BGB-290 40 mg PO BID. The most common adverse event (AE) considered related to both study drugs was fatigue. Immune-related AEs of Grade ≥3 were elevated alanine aminotransferase/aspartate aminotransferase (n = 3), autoimmune hepatitis (n = 3), and hepatitis (n = 1). Complete or partial response was observed in 11 patients, 4 of whom had confirmed PR or CR. Plasma/serum exposure of BGB-290 and BGB-A317 were consistent with those in single-agent trials. Conclusions: The combination of BGB-A317 and BGB-290 was generally well tolerated in patients with advanced solid tumors. These results support the continuation of this trial with enrollment into the disease-specific cohorts. Clinical trial information: NCT02660034