Baseline biomarker analysis and clinical outcomes of the PD-1/TGFβR2 bispecific antibody INCA33890 in patients with non-MSI-H metastatic colorectal cancer (mCRC).

186 Background: INCA33890 is an anti–PD-1/TGFβR2 bispecific antibody designed to antagonize TGFβR2/PD-1 signaling in immune cells co-expressing both targets. In the INCA33890-101 study (NCT05836324), patients (pts) with refractory non-MSI-H mCRC were treated with INCA33890 monotherapy at 3 expansion doses. Responses were observed in pts with and without active liver metastases. Here, we analyze associations between baseline biomarkers and clinical outcomes. Methods: Fresh or archival (≤3 years from study registration) baseline biopsies were required in the dose expansion part and assessed using immunohistochemistry (IHC) for CD8 and PD-L1 (SP263) and whole transcriptome and next-generation sequencing for DNA aberrations (both Tempus xT). Baseline ctDNA was analyzed using Predicine Atlas during dose escalation and expansion. Efficacy was assessed by investigators per RECIST v1.1. Results: As of July 25, 2025, efficacy data with INCA33890 monotherapy were available from 105 pts; 16 pts (15.2%) had a partial response (PR), including pts with liver and peritoneal metastases (Table). Of the 78 pts with evaluable baseline biopsies for IHC analysis, pts with PR or stable disease (SD) showed greater PD-L1 tumor area positivity scores than those with progressive disease (PD) (nominal p20 mut/MB had a trend towards higher ORR (33.3%) vs pts with bTMB 1% 56 17.9 25.0 PD-L1 TAP >5% 13 38.5 61.5 bTMB high >20 mut/MB 15 33.3 40.0 bTMB <20 mut/MB 64 12.5 28.1