Zentalis Pharmaceuticals, Inc. 8-K

What Happened Zentalis Pharmaceuticals announced on May 21, 2026 (8-K filed same day) that data from Part 1 of its Phase 1b MUIR trial of azenosertib combined with chemotherapy will be presented at the ASCO Annual Meeting (May 29–June 2, 2026). The reported results (data cutoff Dec 1, 2025) cover 46 patients with platinum-resistant ovarian cancer across four dose cohorts (200 mg QD continuous; 200, 250, 300 mg QD intermittent 5 days on/2 days off) combined with paclitaxel 80 mg/m². The company also furnished a press release with the 8-K.

Key Details

• Population and timing: 46 patients in an all-comer PROC population; data cutoff Dec 1, 2025; ASCO presentation scheduled May 29–June 2, 2026.
• Efficacy (all cohorts, n=46): Overall Response Rate (ORR) 39.1% (95% CI: 25.1–54.6); Clinical Benefit Rate (CBR) 58.7% (95% CI: 42.2–73.0); median Duration of Response (DOR) 5.6 months; median Progression-Free Survival (PFS) 7.3 months.
• 250 mg intermittent cohort (n=12): ORR 50.0% (one complete response); CBR 66.7%; median DOR 9.2 months; median PFS 5.5 months — highlighted as the potential optimal therapeutic index.
• Safety: most common treatment-related adverse events (all grades) were fatigue (60.9%), anemia (58.7%), nausea (52.2%), neutropenia (50.0%). Grade ≥3 TRAEs: neutropenia 30.4%, anemia 19.6%. Serious TRAEs occurred in ~20% of patients; one investigator-assessed Grade 5 sepsis event previously reported (June 2024).

Why It Matters These Phase 1b results provide early clinical evidence that azenosertib combined with paclitaxel has activity in platinum-resistant ovarian cancer across biomarker subgroups (Cyclin E1–positive and –negative) and identify a 250 mg intermittent dosing schedule as a promising dose for further study. For investors, the update is material because Zentalis’ pipeline and future prospects are substantially tied to azenosertib’s clinical development; the company flagged that additional combination-arm data will be presented later and included standard forward-looking statement cautions. The data are preliminary (small patient numbers, Phase 1b) and subject to change as more patients and follow-up are reported.