Phase II Triple Combo Trial of Osemitamab for Gastric/Gastroesophageal Adenocarcinoma Produces Encouraging Results


Results showed median progression-free survival reached 12.6 months in patients with CLDN18.2 high or medium expression, including in patients with PD-L1 CPS<5.

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Transcenta has announced results from the Phase I/IIa Cohort-G data for Osemitamab (TST001) plus Nivolumab and CAPOX as the first-line treatment of patients with advanced gastric or gastroesophageal (G/GEJ) adenocarcinoma. Data from the study showed encouraging results for the triple combination, especially in patients with high or medium (H/M) CLDN18.2 expression, regardless of their PD-L1 CPS value.1

According to the results, median progression-free survival (mPFS) reached 12.6 months in patients with H/M CLDN18.2 expression, any PD-L1 CPS, as well as in the 80% of patients with PD-L1 CPS<5. Using the group of patients with very low/no CLDN18.2 expression as surrogate control, the HR for the triple combination is 0.443 (95%CI, 0.205-0.958) in favor of the H/M expressors and in these patients, the confirmed overall response rate was 68%.

"These Phase II results mark a significant milestone for Osemitamab (TST001) as this data continues to demonstrate significant anti-tumor activities, particularly in patients with high or medium CLDN18.2 expression, including in those with PD-L1 CPS<5, which is consistent with our preclinical data and mechanistic hypothesis," Caroline Germa, MD, executive vice president, global medicine development and chief medical officer at Transcenta said in a press release. "In this population, the triple combo treatment delivered significantly better PFS benefits than that of the doublet combinations of checkpoint inhibitor/chemo or CLDN18.2 targeted antibody plus chemo. These results further validate our strategy for the Global Phase III trial, which received FDA and CDE clearance and continue to advance the progression of Osemitamab (TST001) toward becoming a global therapy that elevates the current standard of care for HER2-negative metastatic G/GEJ adenocarcinoma."

Cohort-G from the Phase I/IIa study, TranStar102 (NCT04495296) enrolled patients regardless of their CLDN18.2 and PD-L1 CPS expression. As of the cut-off date, 82 patients had been dosed with a median follow-up of 12.6 months. Efficacy analysis was performed in the 66 patients with known CLDN18.2 and PD-L1 expression status.

The safety profile of the triplet combination was found to be consistent with safety data of the Osemitamab (TST001)/CAPOX combination in 1L G/GEJ cancer patients from previous research.

In the press release, Professor Lin Shen, director, department of gastrointestinal oncology and Phase I clinical trial center at Peking University Cancer Hospital; and principal investigator of the trial added: "I am excited about these results and the potential they hold for improving the first-line treatment effect and prolonger PFS and OS for patients with HER2-negative metastatic G/GEJ adenocarcinoma."


1. Transcenta Debuts Encouraging Phase II Data from First-line Triple Combo Trial of Osemitamab (TST001) for G/GEJ Cancer at ASCO 2024. News release. May 24, 2024. Accessed May 28, 2024.

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