Clinical-stage biotechnology company Riboscience LLC announced on Monday the presentation of initial overall survival (OS) and immune activation data from the Phase 1a/b clinical trial of RBS2418, its oral inhibitor of ENPP1, at the European Society for Medical Oncology (ESMO) Congress 2026 in Madrid, Spain.

Poster 1977P reported safety, pharmacokinetic, pharmacodynamic, immune activation and overall survival data from 81 subjects with heavily pretreated advanced, metastatic solid tumours who received RBS2418 as monotherapy (n=49) or in combination with pembrolizumab (n=27) or other treatments (n=5).

RBS2418-1001 is a Phase 1a/b, open-label, non-randomised study in adults with advanced, unresectable, recurrent, or metastatic solid tumours that had progressed following, or were ineligible for, standard therapies. RBS2418 is administered orally as monotherapy or in combination with pembrolizumab or other approved cancer therapies. The study is currently ongoing in Phase 1b, with open cohorts in selected tumour types.

The data showed median overall survival of 12 months with RBS2418 monotherapy in subjects with heavily pretreated tumours that express ENPP1 and cGAS proteins (TME-EG+ phenotype), versus 4.2 months in subjects whose tumours do not (median 3 prior systemic therapies). Median overall survival was 14 months in heavily pretreated TME-EG+ late-line metastatic colorectal cancer (mCRC, median 4 prior systemic therapies), including subjects with liver metastases.

RBS2418 was safe and well tolerated in the safety population of 89 treated subjects. No treatment-related serious adverse events or treatment discontinuations were reported.

Riboscience said that the results support continued development of RBS2418. RBS2418 is being evaluated in two ongoing Phase 2 studies: as monotherapy in late-line mCRC, and in combination with the STRIDE regimen (tremelimumab plus durvalumab) as first-line treatment for hepatocellular carcinoma.