Most common D + T + CAPOX regimen related TEAEs were G1/2: anemia, thrombocytopenia, fatigue, diarrhea, nausea each in 3 pts. No related G3/4 toxicities; overall four G5 events; 1 related event pulmonary embolism. mITT analysis included 22 pts. Preliminary ORR in response evaluable (RE) mITT was 68% (13 PR, 6 SD, 1 NE, 2 pending first scan) and DCR 100%. In RE DKK1 high pts (n¼7) there was an ORR of 100% (6 PR, 1 NE) compared with DKK1 low pts (n¼9) ORR of 56% (5 PR, 4 SD). Median DoR and PFS were not reached.Conclusions: D + T + CAPOX was well tolerated and has encouraging early activity as first line treatment for advanced GEA (unselected for PD-L1), with a preliminary ORR of 68% and DCR of 100%. Higher ORR in biomarker RE population: DKK1 high compared with DKK1 low (ORR 100% vs 56%). Updated ORR, DoR, PFS and PD-L1 expression will be reported.Clinical trial identification: NCT04363801.

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