Impact of WNT/B-catenin alterations and metastasis location among patients with metastatic colorectal cancer (mCRC) treated with immune checkpoint inhibitors (ICI) combinations

3573 Background: Emerging evidence suggests that WNT mutations and liver/peritoneal metastases in mCRC may have an immunosuppressive role that could affect ICI activity. Aim: To evaluate the impact of WNT alterations and liver/peritoneal metastasis among patients with mCRC treated with ICi. Methods: Patients from Vall d’Hebron Hospital, with mCRC treated with ICI from 2017-2022 were included. WNT alterations (APC, AXIN1/2, CTNNB1, FBXW7, EPHB2, RNF43 and SOX9) were evaluated using NGS (tissue). Clinical outcomes were calculated using survival Kaplan-Meier curves. Patients' characteristics were collected retrospectively. Results: Overall, 104 patients were included (66 MSI patients and 38 MSS patients). Among MSI patients, median age was 63 years (22-95), with 53% female, and 64% of patients received immunotherapy in 1st or 2nd line. Regarding tumor characteristics, 72% were right-sided and 82% harbored WNT alterations. 75% of patients presented with liver/peritoneal metastases. Patients with WNT mutations and peritoneal/liver metastases exhibit lower ORR (46% vs 57% p 0.5 and 45% vs 75%, p 0.03 respectively). Peritoneal/liver metastases were associated with lower PFS (HR 3.6 CI95% 1.27-10.24 p 0.02 respectively). Overall, tumors with WNT pathway alterations tend to have shorter PFS and OS. Liver metastases were associated with lower OS (NR vs 34 months HR 2.49 CI95% 1.01-6.17 p 0.05). Table summarizes outcomes. Among MSS patients, median age was 57 years (41-75), with 25% female and 92% of patients receiving immunotherapy > = 3rd line. Regarding tumor characteristics, 78% were left-sided and 90% harboured WNT alterations. 79%, of patients presented with liver or peritoneal metastases. WNT mutations were not associated with ORR, patients without liver/peritoneal metastases tend to have higher ORR (12.5% vs 3.3% p 0.335). Patients with WNT alterations had worse PFS (9.23 vs 1.87 months, p 0.12), and liver metastases were associated with lower PFS (6.98 vs 1.79 months HR 2.87 CI95% 1.17-7.09 p:0.02). Regarding OS, tumors harboring WNT alterations have shorter OS (8.4 vs 12 months p 0.63). The presence of liver or peritoneal metastases was associated with lower OS (NR vs 7.85 months HR 3.69 CI95% 1.09-12.55 p: 0.04). Conclusions: In our cohort, WNT pathway mutations, and liver metastases were associated with worse ORR, PFS, and OS regardless of MSI status. These findings need further validation in a prospective cohort. [Table: see text]