ZNTL · Zentalis Pharmaceuticals, Inc.

This 8-K filing conveys high-materiality scientific and clinical validation for Zentalis’ lead asset, azenosertib, through two AACR 2026 poster presentations. The preclinical data in TNBC — particularly the 87.5% complete response rate with azenosertib + EV in an ADC-resistant PDX model — directly addresses a growing unmet need as antibody-drug conjugates advance into earlier lines of therapy. The robust monotherapy activity across 12 diverse TNBC models, including those with PARP inhibitor resistance, strengthens the biological rationale for WEE1 inhibition in replication-stressed tumors. Critically, the real-world analysis from two independent cohorts confirms that Cyclin E1 protein positivity — irrespective of CCNE1 amplification status — is a consistent, clinically meaningful prognostic factor in ovarian cancer, with statistically significant reductions in time to next treatment. This reinforces the biomarker-stratified development strategy underlying the ongoing DENALI and ASPENOVA registration trials in Cyclin E1-positive platinum-resistant ovarian cancer. The data collectively de-risk the expansion hypothesis for azenosertib into TNBC while simultaneously strengthening the clinical urgency and differentiation for its primary ovarian cancer indication. No financial results, executive changes, agreements, or financing events are disclosed; the materiality stems entirely from the strength, specificity, and clinical alignment of the presented preclinical and real-world evidence.