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

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). In addition to the recently announced 75% response rate in the 1L patient group (including 1 CR and 8 PR), 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 31 March 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 favourably with historically reported PFS outcomes for standard-of-care pembrolizumab monotherapy and pembrolizumab plus chemotherapy, TiumBio said. 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, with a substantial proportion of patients remaining alive and continuing on treatment or follow-up at the time of analysis.

The findings suggest that the Tosposertib and Keytruda combination may offer meaningful clinical advantage even in later-line patients who have limited treatment options after failure of existing therapies.