Facts and hopes in colorectal cancer immunotherapy.

Although a minority of colorectal cancers exhibit mismatch-repair deficiency and associated sensitivity to immune checkpoint inhibitors, the vast majority of colorectal cancers arise in a tolerogenic microenvironment with mismatch-repair proficiency, low tumor-intrinsic immunogenicity, and negligible immunotherapy responsiveness. Treatment strategies to augment tumor immunity with combination immune checkpoint inhibitors and chemotherapy have broadly failed in mismatch-repair proficient tumors. Similarly, although several small single-arm studies have shown that checkpoint blockade plus radiation or select tyrosine kinase inhibition may show improved outcomes compared to historical controls, this finding has not been clearly validated in randomized trials. An evolving next generation of intelligently engineered checkpoint inhibitors, bispecific T-cell engagers, and emerging CAR-T cell therapies may improve immunorecognition of colorectal tumors. Across these modalities, ongoing translational efforts to better define patient populations and biomarkers associated with immune response, as well as combine biologically-sound and mutually-amplifying therapies show promise for a new era of immunotherapy in colorectal cancer.