Immune checkpoint inhibitors, which unleash the immune response against tumor cells, have revolutionized cancer treatment; however, the medications aren’t effective in a large number of patients, including those with colorectal cancer. New research published in PNAS that was led by investigators at Massachusetts General Hospital (MGH) and the University of Geneva (UNIGE) provides insights on why some types of colorectal cancer don’t respond to immune checkpoint inhibitors and offers a strategy to overcome their resistance.