Zetagen Therapeutics to Present Preliminary Results from Phase 2 Clinical Trial Targeting Metastatic Breast Cancer to Bone at the 2025 San Antonio Breast Cancer Symposium

Complete Response in all treated lesions: Patients completing the study showed CR via the MD Anderson Criteria and RECIST v1.1 with no active tumor detected on MRIFirst-of-its-kind single intratumoral injection for MBC to the spineTreated lesions showed full bone regeneration with reconstitution of trabecular bone, and no skeletal related events; mean lesion defect volume decreased by 87.9% at day 180.Therapeutic spread extended to nearby non-treated lesions, also achieving complete response within the same vertebral body

Zetagen Therapeutics, a privately held clinical-stage biopharmaceutical company pioneering first-of-its-kind targeted therapies for both primary and metastatic breast cancer, announced today that its abstract titled “Single Intratumoral Drug Injection Yields Complete Response (CR) in Metastatic Breast Cancer (MBC) Bone Lesions”, has been accepted and will be presented at the 2025 San Antonio Breast Cancer Symposium (SABCS) on Wednesday, December 10, 2025.

The abstract presents preliminary clinical data from a recently completed Phase 2a trial (NCT05280067) performed at the University of British Columbia evaluating ZetaMet™ (Zeta-BC-003) for safety and efficacy for the treatment of MBC lytic bone lesions in Stage 4 breast cancer patients. Phenotypes treated within the study, TNBC, HR+, HR+/HER2+, and HERS2+/HR-. Each patient underwent a single fluoroscopy-guided injection of ZetaMet™ while under sedation. All achieved a complete response (CR), ceased tumor activity, with no serious adverse events (SAEs), adverse events (AEs), or skeletal-related events (SREs) and many demonstrated a reconstitution of trabecular bone, which further underscores the potential of ZetaMet™ to not only halt disease progression but restore skeletal integrity.

The findings build on prior compassionate use cases published in peer-reviewed journals with two-year follow-up, reinforcing ZetaMet’s™ potential to prevent SREs and improve overall survival. The abstract will be published in SABCS 2025 Proceedings and featured in Clinical Cancer Research.

With the trial now complete and comprehensive analyses underway, this presentation at SABCS will represent the most detailed data release to date. A full report of the findings will also be submitted to Health Canada (HC) and the U.S. Food and Drug Administration (FDA) to inform future planning discussions.

Presentation Details:

• Abstract Number: 3549
• Presentation Number: PS1-13-18
• Presentation Title:Single Intratumoral Drug Injection Yields Complete Response in Metastatic Breast Cancer Bone Lesions: Results from Phase 2a Trial
• Poster Presentation: Wednesday, December 10, 2025, 12:30-2:00pm CST

“The promising Phase 2a findings for ZetaMet™ mirror our earlier peer-reviewed results, reinforcing the strength of our clinically validated strategy in treating metastatic breast cancer,” said Joe C. Loy, CEO of Zetagen Therapeutics. “We observed that both treated and adjacent non-treated lesions within the same vertebral body achieved complete response, with no signs of tumor activity and no skeletal-related events—all using the same drug concentration validated in our preclinical studies—strongly affirming the scientific foundation of our approach.”

About ZetaMet™ (Zeta-BC-003)

ZetaMet™ (Zeta-BC-003) is the first-of-its-kind, synthetic, small-molecule, administered intratumorally to minimize off target toxicity, delivered via a proprietary controlled-release carrier intended to resolve metastatic breast cancer bone lesions, inhibit pain while regenerating bone, with the potential to increase survival rates.

The US Food & Drug Administration (FDA) has recognized Zetagen’s discoveries with multiple Breakthrough Designations including ZetaMet™.

Zetagen with FDA and Health Canada (HC) approval via the Expanded Access (Compassionate Use) program has treated eight (8) patients with ZetaMet™ (Zeta-BC-003) with results published in multiple peer-reviewed journals.

Peer-reviewed 2-year follow up clinical data published in 2023 on ZetaMet™ (Zeta-BC-003) demonstrated resolution of seven (7) lytic lesions (radiated and non-radiated), reduction in pain, significant attrition of opioid pain medication (4-fold), prevention of vertebral fracture, and increased survival rate in a patient living with Stage 4 breast cancer.ⁱ To view this publication via open access, go to: https://www.tandfonline.com/doi/full/10.2217/pmt-2023-0069

About Zetagen Therapeutics

Zetagen has three novel drugs in development with the Zeta Platform, ZetaMet™ (Zeta-BC-003), for the treatment of metastatic breast cancer to bone, ZetaMast™ (Zeta-MBC-005) for breast cancer liver metastases (BCLM), and ZetaPrime™ (Zeta-PBC-007) for the treatment of primary HR+ breast cancer, all with inspiring results. To learn more, visit www.zetagen.com. The entire Zeta platform is designed for intratumoral administration to reduce off-target toxicity, utilizing proprietary carriers—some incorporating our New Molecular Entity. The USPTO has granted Zetagen Composition-of-Matter patents and claims for all three therapeutics.

Zetagen Upcoming Events

Zetagen will attend the 2025 San Antonio Breast Cancer Symposium (SABCS) and the 2026 JP Morgan Healthcare Conference.

Forward-Looking Statements

This press release contains certain forward-looking statements with the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934 and Private Securities Litigation Reform Act, as amended, including those relating to the Company’s product development, clinical and regulatory timelines, market opportunity, competitive position, possible or assumed future results of operations, business strategies, potential growth opportunities and other statements that are predictive in nature. These forward-looking statements are based on current expectations, estimates, forecasts and projections about the industry and markets in which we operate and management’s current beliefs and assumptions. Source: Zetagen Therapeutics, Inc.

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ⁱ Pain Management. Volume 13, Issue 10, October 2023, Pages 569-577 https://doi.org/10.2217/pmt-2023-0069

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