Immunotherapy in mismatch repair-deficient metastatic colorectal cancer – Outcome and novel predictive markers

Background: This study aims to assess predictive markers for response to immunotherapy in dMMR/MSI-H metastatic colorectal cancer (mCRC) patients. Materials and methods: A study using two prospective cohorts from MD Anderson Cancer Center and Sheba Medical Center of consecutive patients with dMMR/MSI-H mCRC that were treated with immunotherapy between 2014–2022. Primary outcome was progression-free survival (PFS) and secondary outcome was overall response rate (ORR). Evaluated predictors included ECOG-PS score, RAS/BRAF status, single-agent versus doublet immunotherapy, metastatic sites, disease burden, and CEA levels prior to treatment initiation. Kaplan-Meier analysis and Cox proportional hazard regression model were used to analyze the effect of exposure variables on PFS. Results: The study included 153 patients. Median follow-up time was 26 months (IQR 11–48). Median PFS was 51.6 months (95%CI 38.1-NR) and ORR was 58.1%. In a univariate analysis, male sex was associated with worse PFS with a HR of 1.67 (95% CI 1.00–2.79); Right-sided tumors were associated with improved PFS with a HR of 0.56 (95% CI 0.32–0.97); Liver or lung metastasis were associated with worse PFS with HRs of 2.35 (95%CI 1.43–3.88) and 2.30 (95%CI 1.31–4.04), respectively; ECOG-PS score ≥ 2, CEA levels ˃5 μg/L prior to treatment initiation and ≥ 3 metastatic sites were associated with worse PFS with HRs of 2.09 (95%CI 0.98–4.47), 2.23 (95%CI 1.30–3.81) and 3.11 (95%CI 1.61–6.03), respectively. Liver or lung metastasis remained significant in a multivariable model. Conclusions: Extent of disease (worse PFS with high CEA, poor ECOG-PS and ≥3 metastatic sites) and disease location (worse PFS with liver or lung metastasis and left sided tumor) were associated with immunotherapy outcome in dMMR/MSI-H mCRC.