New research is evolving that may revolutionize the way we treat colorectal cancer. About 15% to 20% of patients with localized colon cancer and 5% to 7% of patients with rectal cancer have mismatch repair deficiency (MMRD) (World J Gastrointest Oncol 2020;12:808-832), making them less responsive to conventional chemotherapy but highly responsive to immunotherapy with checkpoint inhibitors.
Studies already have shown the benefit of immunotherapy in patients with MMRD advanced-stage CRC (N Engl J Med 2020;383:2207-2218). Recently published data demonstrate that immunotherapy also could be helpful for patients with localized CRC with MMRD, with trials reporting complete regression of such tumors without chemotherapy, radiation therapy or surgery. Chalabi et al presented results of the NICHE-2 trial of 107 patients with MMRD localized colon cancer at the 2022 annual meeting of the European Society for Medical Oncology, showing that immunotherapy alone could induce complete regression of the tumors in 67% of patients (abstract LBA7). In another study, Cercek et al found that six months of immunotherapy resulted in complete regression of rectal tumors in 12 patients (N Engl J Med 2022;386:2363-2376).