An adverse event (AE) was defined as any untoward medical occurrence associated with the use of a drug in humans, whether or not considered drug related, that occurred after a participant provided informed consent. Abnormal laboratory values or test results occurring after informed consent constituted AEs only if they induced clinical signs or symptoms, were considered clinically meaningful, required therapy (e.g., hematologic abnormality that required transfusion), or required changes in the study drug(s). A TEAE was defined as any AE either reported for the first time or the worsening of a pre-existing event after the first dose of study drug.

A DLT was defined as the occurrence of any protocol-defined toxicity occurring up to and including Day 28, except those with a clear alternative explanation (e.g., disease progression) or transient (≤72 hours) abnormal laboratory values without associated clinically significant signs or symptoms based on investigator determination. All DLTs were assessed by the investigator using Common Terminology Criteria for Adverse Events (CTCAE) v4.03 criteria.

The RP2D of the combination of INCB001158 and chemotherapy in 21-day (for gemcitabine/cisplatin) or 28-day (for mFOLFOX6 or paclitaxel) treatment cycles in participants with advanced or metastatic solid tumors was determined. After the dose escalation was completed, the INCB001158 dose level that was pharmacologically active and tolerable in combination with each chemotherapy regimen (i.e., maximum tolerated dose or lower) was determined to be the RP2D. The RP2D was then further assessed in tumor expansion cohorts in Phase 2.

ORR was defined as the percentage of participants with a best overall response of complete response (CR) or partial response (PR), as determined by investigator assessment of radiographic disease as per Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1 (v1.1). CR: disappearance of all target and non-target lesions and no appearance of any new lesions. Any pathological lymph nodes (whether target or non-target) must have a reduction in the short axis to \<10 millimeters (mm). PR: complete disappearance or at least a 30% decrease in the sum of the diameters of target lesions, taking as a reference the baseline sum diameters, no new lesions, and no progression of non-target lesions. Analysis was conducted by cohort (tumor type) in Phase 2 because different tumor types could have different response criteria or different background response rates.