Background: Adavosertib (AZD1775; A) is a highly selective inhibitor of WEE1. This Phase I study (NCT02617277) investigated a range of doses and schedules for oral A plus IV durvalumab (DV), a human monoclonal antibody targeting PD-L1, to determine the maximum tolerated dose (MTD) and recommended Phase II dose (RP2D) in patients (pts) with advanced solid tumors. Methods: Four 28-day schedules (Sch) were evaluated with pts receiving DV 1500 mg on day (d) 1 of each schedule (Table). Patients continued treatment if they showed clinical benefit in the absence of any discontinuation criteria. Pts received A monotherapy for PK analysis prior to the start of combination therapy in Sch B, C (d –7 to –5) and D (d –9 to –5). MTD was determined using a 3+3 dose-escalation cohort design. Predefined dose-limiting toxicities (DLTs) were evaluated during the first cycle of study treatment. Results: 54 pts received A (most common primary tumor sites: colon, 19%; lung, 13%; breast, 11%). The most common grade ≥3 AEs were fatigue (15%), diarrhea (11%) and nausea (9%). DLTs were nausea (n = 2) and diarrhea (n = 1). 7 pts (13%) had A-related SAEs, including reversible and confounded drug-induced liver injury (Sch B 125 mg and Sch C; 1 each). Disease control rate (DCR) for the total cohort was 36%. Preliminary PK at 150 mg BID suggests adequate coverage for cell kill activity and no drug–drug interaction. Conclusions: The MTD/RP2D was A 150 mg BID (3 d on, 4 d off; treatment d 15–17, 22–24) with DV 1500 mg (d 1 Q4W); safety profile was considered acceptable. Preliminary evidence of antitumor activity was observed. Clinical trial information: NCT02617277

*Only 6 pts received DV; ^†DLT evaluable in 6 pts only