NEW YORK, June 11, 2026 — Leads & Copy — Zetagen Therapeutics has issued a correction to its previously released Phase 2a study results for its investigational drug ZetaMet™ (Zeta BC 003), clarifying that the study reported no treatment-related adverse events, rather than no treatment-emergent adverse events. The correction, issued on June 11, 2026, does not affect any other data from the study. The company expressed regret for the error and aims to ensure accurate communication.
The updated announcement details preliminary topline results from the Phase 2a clinical study of ZetaMet™ in patients with metastatic breast cancer (MBC) who have lytic bone lesions. The study observed no skeletal-related events (SREs) or fractures following a single intratumoral injection of ZetaMet™. Additionally, no treatment-related adverse events (AEs) or serious adverse events (SAEs) were reported. Participants experienced cessation of tumor activity, reduced pain scores, and decreased opioid consumption. Notably, a therapeutic effect was observed in adjacent, non-injected lesions within the treated vertebral body.
Zetagen Therapeutics, a biopharmaceutical company focused on novel therapies for primary and metastatic breast cancer, presented these findings at the American Society of Clinical Oncology (ASCO) Annual Meeting on Monday, June 2, 2026. ZetaMet™ (Zeta BC 003) is an investigational product that has received Breakthrough Designation from the U.S. Food and Drug Administration (FDA) but has not yet been approved by the FDA or any other regulatory authority.
Joe C. Loy, President & CEO of Zetagen Therapeutics, stated, “We are encouraged by the preliminary findings from this Phase 2a study, which provide important clinical observations on the investigational use of ZetaMet™ in patients with metastatic breast cancer involving bone. These results also highlight a major achievement for our team, overcoming longstanding industry challenges in intratumoral administration by developing proprietary carriers which deliver compounds that demonstrate solubility and localized bio-adhesion.”
The preliminary findings were presented by Dr. Bryan Margulies, Chief Scientific Officer, and Joe C. Loy. The abstract can be accessed at https://doi.org/10.1200/JCO.2026.44.16_suppl.589.
The open-label Phase 2a study, identified as ZGMBC (NCT05280067), was conducted at the University of British Columbia and enrolled 10 subjects with a mean age of 52. The participants represented various MBC subtypes: HR+ (n=6), HR+/HER2+ (n=2), HER2+/HR– (n=1), and TNBC (n=1). Five subjects had breakthrough lytic lesions despite prior bisphosphonate therapy. One subject passed away due to pleural edema, which was determined to be unrelated to the study treatment. A total of 11 target lesions received a single intratumoral injection of Zeta BC 003 under sedation, and four adjacent, non-injected lesions were also evaluated.
Contextualizing the findings, historical literature indicates SRE rates of approximately 53% in metastatic breast cancer with bone involvement under conventional therapy, with SREs, particularly fractures, associated with a reduction in overall survival by about 4.8 months. In the observed study findings, there were no reported SREs or fractures. Tumor activity ceased within treated vertebral bodies, and therapeutic spread was observed to adjacent, untreated lesions within the same vertebral body. No treatment-related AEs or SAEs were reported.
Further quantitative results showed a mean bone defect volume decrease of 65.4% at Day 84 (±20.5%; p=0.0003) and 84.1% at Day 180 (±13.1%; p<0.0001). Pain scores (NRS) decreased by an average of 4.16 points (p<0.05), and opioid use (MED) decreased by 33–67% among opioid-treated subjects. Spinal stability (SINS) improved by 18.5% (p<0.05). Quality of life also improved, with the Physical Component Summary (PCS) increasing by 24.2% and the Mental Component Summary (MCS) increasing by 12.1%.
While cross-study comparisons have limitations, the absence of AEs and SREs in this Phase 2a study supports continued investigation. These observations align with two published Expanded Access case reports (seven lesions, 2-year follow-up) that also demonstrated the absence of SREs, cessation of tumor activity, neo-trabecular bone formation, and therapeutic spread within treated vertebral bodies.
Zetagen Therapeutics acknowledged the contributions of its clinical partners: the University of British Columbia, Nor Consult, LLC (NorCo), and Medical Medics Incorporated. NorCo provided clinical operations support, and Medical Medics provided centralized imaging services.
ZetaMet™ is designed for single intratumoral administration into lytic bone lesions associated with metastatic breast cancer. Preclinical and clinical studies suggest its potential to cease lytic activity, reduce pain, initiate bone healing, and prevent SREs, though it remains unapproved by regulatory authorities.
About Zetagen Therapeutics: Zetagen Therapeutics is a clinical-stage biopharmaceutical company developing novel therapies for primary and metastatic breast cancer. Their “Zeta”‑platform is engineered to overcome intratumoral delivery challenges using proprietary carriers and New Molecular Entities (NMEs) to enhance compound solubility and localized bio-adhesion, aiming to minimize off-target toxicity.
Source: Business Wire
