With TMB ≥9 or BRAF-V600E and normal, non-inflammatory level of C-reactive protein when starting nivolumab (n = 11), median PFS was 35.0 months (95% confidence interval, 6.8-63.0; p < 0.0001).<h4>Conclusions</h4>TMB, somatic BRAF status and systemic inflammation should be prospectively investigated as practical biomarkers for predicting potential responsiveness to immune checkpoint inhibitors in metastatic microsatellite-stable/mismatch repair-proficient colorectal cancer. Here, CRP is linked to colorectal cancer.