Zentalis reports 15.9-month median OS for azenosertib in PROC at ESMO
Zentalis Pharmaceuticals has presented the first overall survival analysis for its WEE1 inhibitor azenosertib at the European Society for Medical Oncology Congress 2026 in Madrid, with interim data from the DENALI Part 1b study showing a median overall survival of 15.9 months in Cyclin E1-positive platinum-resistant ovarian cancer patients.
The dataset, drawn from 102 heavily pretreated patients enrolled in the Phase 2 DENALI study (NCT05128825, GOG-3066) as of a May 2026 data cutoff, also showed a median OS of just 7.5 months in the Cyclin E1-negative subgroup. The near doubling of survival in the biomarker-selected population represents the headline finding and is being used by Zentalis to justify a prospective biomarker-enrichment strategy in its ongoing registration-intent studies.
The data in detail
Of 94 evaluable patients with known Cyclin E1 status, 48 were classified as IHC-positive and 46 as IHC-negative. In the IHC-positive group, 31 of 48 patients had died at data cutoff, giving a median OS of 15.9 months (95% CI, 8.7 to 21.2). In the IHC-negative group, 34 of 46 patients had died, yielding a median OS of 7.5 months (95% CI, 5.8 to 12.3).
Objective response rate in response-evaluable Cyclin E1-positive patients stood at 37.2%, with median duration of response of 5.5 months, though two patients showed durable responses exceeding 15 and 20 months respectively.
The patient population was notably pre-treated: 97% had received a taxane, 91% bevacizumab, 55% a PARP inhibitor, and 15% mirvetuximab soravtansine, with a median of three prior lines of therapy. The median relative dose intensity of 84.6% indicates patients maintained meaningful drug exposure despite frequent dose modifications; 56.9% required a dose interruption and 43.1% a dose reduction during the study.
Safety was consistent with prior reporting. Grade 3 or higher non-haematologic toxicity was led by fatigue at 16%, while haematologic toxicities included thrombocytopenia, anaemia, and neutropenia, each at approximately 11 to 12%. Discontinuation due to treatment-related adverse events occurred in 19.6% of patients.
Fiona Simpkins, Professor at the University of Pennsylvania Perelman School of Medicine and lead DENALI investigator, said the survival separation "strongly supports Cyclin E1 protein expression as a clinically relevant and predictive patient selection biomarker for azenosertib."
Market context and regulatory path
Platinum-resistant ovarian cancer remains one of gynaecological oncology's most intractable settings. The only biomarker-selected approval in the adjacent space is mirvetuximab soravtansine, which targets FRa-high tumours. No therapy has yet received regulatory clearance specifically in Cyclin E1-positive PROC, which Zentalis estimates represents roughly half of all platinum-resistant cases.
The WEE1 inhibitor class has had a difficult development history; earlier compounds were limited by toxicity, and Zentalis' 5:2 intermittent dosing schedule is partly designed to address that historical weakness. The OS data from DENALI Part 1b will be scrutinised by regulators in the context of the ongoing ASPENOVA Phase 3 trial, which is designed to support full approval and is randomising approximately 420 patients against investigator's choice of standard-of-care chemotherapy, with progression-free survival as the primary endpoint.
DENALI Part 2, the registration-intended single-arm cohort, is pursuing accelerated approval pending positive outcomes and further FDA alignment. Part 2b enrolment is complete; Part 2c, targeting taxane-pretreated patients, is currently enrolling. Near-term milestones include a regulatory update on the accelerated approval pathway and top-line data from Part 2b, both of which will be closely watched by investors and the broader ovarian cancer community.