1. Peking University Cancer Hospital. 2. Investigator. 3. Sponsor employee.

Background:

Osemitamab is a humanized monoclonal antibody with improved affinity to claudin 18.2 (CLDN18.2) and has been observed to upregulate PD-L1 expression on CLDN18.2-positive tumor cells.

In vivo anti-tumor activity of osemitamab + anti-PD-1/PD-L1 antibody + chemotherapy was significantly stronger than any of the doublet combinations, regardless of PD-L1 CPS levels, making the triplet of osemitamab, nivolumab and CAPOX an attractive combination.

Promising efficacy of osemitamab plus CAPOX and nivolumab as first-line treatment for gastric or gastroesophageal junction (G/GEJ) cancer has been observed and reported previously at ASCO 2025. Here we report the exploratory efficacy analysis based on CLDN18.2 and PD-L1 expressions

Conclusions:

The updated data indicate that the combination of TST001 plus nivolumab and CAPOX for first-line treatment of patients with G/GEJ cancer is safe and well tolerated.

The exploratory efficacy analysis indicates that encouraging benefit of osemitamab in combination with standard of care in patients with G/GEJ cancer and the potential treatment benefit of osemitamab is consistent regardless of PD-L1 expression.