• 75.0% Response Rate and Median PFS of 10.9 Months Observed in First-Line Recurrent or Metastatic Head and Neck Cancer(R/M HNSCC)
• Advancing Tosposertib Toward Next-Stage Development as a Potential Best-in-Class Treatment Option

SEONGNAM, South Korea, May 31, 2026 /PRNewswire/ — TiumBio Co., Ltd. (KOSDAQ: 321550), a clinical-stage biopharmaceutical company focused on discovering and developing innovative therapeutics, announced clinical data for Tosposertib (TU2218), an oral dual inhibitor targeting transforming growth factor-beta (TGF-β) and vascular endothelial growth factor (VEGF), in first-line (1L) recurrent or metastatic head and neck squamous cell carcinoma (R/M HNSCC) at American Society of Clinical Oncology (ASCO) 2026.

The data presented during the poster session included the latest results and follow-up data from the Phase 2a trial evaluating the combination of Tosposertib and Keytruda (Pembrolizumab) as. In addition to the 75% response rate in the first-line (1L) patient group (including 1 CR and 8 PR), which drew attention upon abstract release on May 22, the presentation also disclosed progression-free survival (mPFS) and overall survival (mOS) data for the first time.

According to the research poster presented by Tiumbio at ASCO 2026, as of the data cutoff date of March 31, 2026, the median progression-free survival (mPFS*) in a total of 12 first-line (1L) patients was 10.9 months. While cross-trial comparisons are inherently limited, this result compares favorably with historically reported PFS outcomes for standard-of-care pembrolizumab monotherapy and pembrolizumab plus chemotherapy. In addition, an 83% response rate was observed in the high CPS (>20) subgroup (n=6), while a 67% response rate was also observed in the low CPS 1–19 subgroup (n=6), a patient population that may derive relatively limited benefit from immuno-oncology therapies.

The median overall survival (mOS*) had not yet been reached (NR), with a substantial proportion of patients remaining alive and continuing on treatment or follow-up at the time of analysis.

The dataset included 14 patients receiving 2^nd-line or later treatment after relapse following prior standard therapy. In this subgroup, the combination achieved a response rate of 42.9% (including 1CR and 5 PR). The mPFS was 2.9 months, while mOS had not yet been reached (NR). By comparison, currently available standard treatment options in 2^nd-line or later settings for R/M HNSCC typically show response rates of approximately 10% to 15%, with mPFS of 2.1 months. These findings suggest that Tosposertib and Keytruda combination may offer meaningful clinical advantage even in later-line patients who have limited treatment options after failure of existing therapies.

In addition, the combination was generally manageable, and safety findings were generally consistent with the known profiles of the agents and the underlying patient population. The incidence of Grade 3 or higher treatment-related adverse events (TRAEs) observed with the combination of Tosposertib and Keytruda was 48.3%. No Grade 5 treatment-related adverse events leading to patient death or cardiovascular toxicities were reported.

Professor Hye Ryun Kim of the Division of Medical Oncology at Yonsei University Severance Hospital, one of Korea’s leading experts in head and neck cancer treatment and the first author who personally presented the poster at ASCO, commented, “The interim data presented at ASCO 2026 represents a differentiated clinical outcome that highlights the potential therapeutic benefit of Tosposertib in recurrent or metastatic head and neck cancer. In this disease setting, where treatment remains challenging and patient prognosis is often poor, we believe Tosposertib has significant potential to emerge as a new treatment option capable of addressing the limitations of existing therapies.” 

Hun-taek Kim, CEO of Tiumbio, stated, “We believe these interim data presented at ASCO 2026 demonstrated a compelling clinical profile compared with outcomes historically observed with current standard of care. Based on these data, we plan to evaluate potential regulatory pathways, including the possibility of seeking Breakthrough Therapy Designation, as we continue to advance Tosposertib toward its potential to become a new standard of care in R/M HNSCC.”

About Tosposertib (TU2218)
Tosposertib (TU2218) is a highly potent, oral dual inhibitor designed to block the signaling pathways of transforming growth factor-beta (TGF-β) and vascular endothelial growth factor (VEGF), two critical mediators of tumor growth and metastasis. This novel drug candidate was discovered and developed by Tiumbio to enhance the therapeutic efficacy of immune-oncology agents such as Keytruda.

About Tiumbio Co., Ltd.
Tiumbio is dedicated to the discovery and development of innovative therapies that alleviate the burden of serious and debilitating disease. Tiumbio’s mission is to expand hope and improve the quality of life for people through science. For further information, visit our website at www.tiumbio.com/en and connect with us on LinkedIn.

Contacts:

Dong-ho Kang, Head of Corporate Communications & Investor Relations
donghokang@tiumbio.com

Da-ye Song, Manager, Corporate Communications & Investor Relations
dayesong@tiumbio.com

Hyun-kyoung Kim, , Manager, Corporate Communications & Investor Relations
hyunkyoungkim@tiumbio.com

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SOURCE TiumBio