AUSTIN, Texas, June 9, 2026
Zetagen Therapeutics announced preliminary topline results from its Phase 2a clinical study evaluating ZetaMet™ (Zeta BC 003) in patients with metastatic breast cancer (MBC) and lytic bone lesions. The investigational therapy demonstrated encouraging clinical outcomes following a single intratumoral injection, including the absence of skeletal-related events (SREs) and fractures, no treatment-emergent adverse events (AEs) or serious adverse events (SAEs), and evidence of halted tumor activity within treated vertebral bodies. The findings were presented at the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting and support the continued clinical development of the FDA Breakthrough Designation candidate.
Phase 2a Study Demonstrates Strong Safety and Clinical Activity
The open-label Phase 2a study enrolled 10 metastatic breast cancer patients with various disease subtypes, including HR-positive, HER2-positive, and triple-negative breast cancer. Across the study, 11 target lesions received a single intratumoral injection of Zeta BC 003, while four adjacent untreated lesions were also monitored. Investigators reported no skeletal-related events, fractures, treatment-emergent adverse events, or serious adverse events during the study period. Additionally, tumor activity ceased within treated vertebral bodies, while therapeutic effects were also observed in adjacent, non-injected lesions located within the same vertebral body, suggesting potential local therapeutic spread.
Significant Improvements Observed in Bone Healing and Pain Reduction
Clinical assessments showed substantial improvements across multiple efficacy measures. Mean bone defect volume decreased by 65.4% at Day 84 and 84.1% at Day 180, indicating significant bone regeneration and healing. Patients also experienced meaningful symptom relief, with pain scores declining by an average of 4.16 points and opioid consumption decreasing between 33% and 67% among opioid-treated participants. Spinal stability improved by 18.5%, while quality-of-life measures demonstrated gains in both physical and mental health scores, highlighting the therapy’s potential impact on patient well-being.
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Findings Support Continued Development of ZetaMet
The results build upon previously published Expanded Access case reports that similarly demonstrated cessation of tumor activity, prevention of skeletal-related events, and evidence of new bone formation following treatment. ZetaMet is being developed as a single-administration therapy designed to target lytic bone lesions associated with metastatic breast cancer while minimizing systemic exposure through localized delivery. Based on the favorable safety profile and encouraging efficacy signals observed in the Phase 2a study, Zetagen Therapeutics plans to continue advancing the program as a potential treatment option for patients with metastatic breast cancer involving bone.
Source: Zetagen Therapeutics press release
