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Get filing alertsZentalis reports 39% response rate in Phase 1b ovarian cancer trial, optimal dose shows 50% ORR
Filed May 21, 2026 · Period ending May 21, 2026 · ~1 min read
Key Changes
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Phase 1b MUIR trial of azenosertib plus paclitaxel showed 39.1% overall response rate and 7.3-month median progression-free survival in 46 platinum-resistant ovarian cancer patients, with results to be presented at ASCO 2026.
Press Release, May 21, 2026 view on EDGAR → -
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Optimal 250mg intermittent dose cohort achieved 50% response rate including one complete response, with 9.2-month median duration of response in 12 patients, establishing preferred dose for future development.
Press Release, May 21, 2026 view on EDGAR → -
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Drug showed similar efficacy in Cyclin E1-positive and negative patients (41.4% vs 35.7% response rates), suggesting broader patient population may benefit beyond biomarker-selected groups when combined with chemotherapy.
Press Release, May 21, 2026 view on EDGAR → -
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Safety profile was manageable with most common side effects being fatigue (60.9%), anemia (58.7%), and neutropenia (50.0%); high-grade events were infrequent. One previously reported death from sepsis was assessed as potentially treatment-related.
Press Release, May 21, 2026 view on EDGAR →
Summary
Zentalis announced positive Phase 1b clinical trial results for azenosertib combined with paclitaxel in platinum-resistant ovarian cancer, a difficult-to-treat patient population. The trial demonstrated a 39% overall response rate across all dose levels, with the optimal 250mg intermittent dosing schedule showing even stronger results at 50% response rate including one complete response.
The 7.3-month median progression-free survival compares favorably to typical outcomes in this heavily pre-treated population. Retail investors should note two key findings: first, the identification of an optimal dose with strong efficacy signals positions the drug for potential Phase 2 development.
Second, the drug worked similarly well regardless of Cyclin E1 biomarker status, potentially expanding the addressable market beyond a biomarker-selected subset. The safety profile appears manageable with mostly low-grade side effects, though one treatment-related death occurred. Watch for the full ASCO presentation in late May/early June 2026 for additional details on patient characteristics, durability of responses, and any commentary on next development steps. The company will likely need to announce plans for a Phase 2 trial to advance this combination toward potential approval.
Section-by-Section Diff
Event · Item 7.01 — Regulation FD Disclosure
Zentalis issued a press release under Regulation FD; no material business event disclosed in the 8-K body itself.
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On May 21, 2026, Zentalis Pharmaceuticals, Inc. (“Zentalis” or the “Company”) issued the press release furnished as Exhibit 99.1 to this Current Report on Form 8-K (the “Current Report”) and incorporated herein by reference.
The company issued a press release on May 21, 2026, furnished as Exhibit 99.1. The 8-K body does not describe the press release content; it only references the exhibit. This is a procedural Regulation FD disclosure with no substantive detail provided in the filing text itself.
Event · Item 8.01 — Other Events
Item 8.01 — Other Events filed; see Key Changes for terms.
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At the 250 mg intermittent (5:2) dose cohort (n=12), which demonstrated the potential optimal therapeutic index, the following clinical activity was observed: •ORR: 50.0% (95% CI: 21.1–78.9), including one complete response •CBR: 66.7% (95% CI: 34.9-90.1) •Median DOR: 9.2 months (95% CI: 3.8–NE) •Median PFS: 5.5 months (95% CI: 1.7–12.9)
The 250 mg intermittent dosing cohort showed the most promising results with a 50% response rate and one complete response among 12 patients. This dose level is identified as having the potential optimal therapeutic index, suggesting it may be the preferred dose for future development.
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As of the December 1, 2025 data cutoff, a manageable safety profile with a low rate of high-grade events across all four dose cohorts (n=46) was observed: •The most common all-grade treatment-related adverse events (TRAEs): fatigue (60.9%), anemia (58.7%), nausea (52.2%), and neutropenia (50.0%). •The most frequent Grade ≥3 TRAEs: neutropenia (30.4%) and anemia (19.6%); rates of high-grade fatigue and nausea were less than 10%. •Serious TRAEs occurred in approximately 20% of patients; the most frequent were fatigue, diarrhea, and neutropenia, each of which occurred in 2 patients.
The trial showed a manageable safety profile with common side effects being fatigue, anemia, nausea, and neutropenia. High-grade adverse events were relatively infrequent, with neutropenia and anemia being the most common serious events. One patient death due to sepsis was reported and assessed as potentially related to treatment.
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Clinical activity was broadly comparable in Cyclin E1-positive patients (ORR: 41.4% [95% CI: 23.5-61.1]; median PFS: 7.3 months [95% CI: 3.7-9.1]) and Cyclin E1-negative patients (ORR: 35.7% [95% CI: 12.8-64.9]; median PFS: 5.4 months [95% CI: 1.7-NE]), suggesting that Cyclin E1-positive biomarker status may not be required to derive benefit when azenosertib is combined with a cytotoxic agent.
The trial found similar response rates and progression-free survival in both Cyclin E1-positive and Cyclin E1-negative patients. This suggests the drug may work across a broader patient population when combined with chemotherapy, potentially expanding the addressable market beyond biomarker-selected patients.
Added in current filing · verify on EDGAR →
One Grade 5 event due to sepsis was assessed as related to azenosertib by the investigator (previously reported in June 2024). While the role of azenosertib cannot be excluded, the event may have been attributable to the patient's advanced disease, given the absence of neutropenia and negative blood cultures at the time of the event.
One patient death occurred due to sepsis that was assessed as potentially related to azenosertib treatment. The company notes this event was previously reported in June 2024 and suggests it may have been due to the patient's advanced disease rather than the drug, though the drug's role cannot be excluded.
Event · Item 9.01 — Financial Statements and Exhibits
Zentalis filed an 8-K to furnish a press release issued May 21, 2026; no material business event disclosed in the filing body.
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The following Exhibit 99.1 relating to Item 7.01 shall be deemed to be furnished, and not filed: Exhibit No. Description 99.1 Press Release issued on May 21, 2026
The company furnished a press release dated May 21, 2026 under Item 7.01. The 8-K body does not disclose the content of the press release, only that it was issued and attached as Exhibit 99.1. Without the exhibit text, no material business event can be identified from this filing.
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