Immunotherapy combined with radiotherapy to reverse immunosuppression in microsatellite stable colorectal cancer

In recent years, the exploration of immune checkpoint inhibitors (ICIs) has resulted in substantial progress and has changed the pattern of cancer treatment. ICIs have revolutionized the treatment landscape of microsatellite instable colorectal cancer while the efficacy is very limited in patients with microsatellite stable colorectal cancer. Therefore, sensitizing MSS CRC to immunotherapy is a major challenge in the field of CRC immunotherapy. Immunotherapy-based combination therapy is an effective strategy. This review of radiotherapy (RT) as a local treatment has dramatically changed in recent years, and it is now widely accepted that RT can deeply reshape the tumor environment by modulating the immune response. Such evidence gives a strong rationale for the synergism of radiotherapy and immunotherapy, introducing the era of ‘immunoradiotherapy’. How to give full play to the synergistic effect of radiotherapy and immunotherapy to improve the therapeutic effect of MSS CRC and bring good prognosis is a hot problem to be solved in the field of cancer treatment.This article reviews the development of CRC immunotherapy, the immune resistance mechanism of MSS CRC, and the impact and potential value of immunotherapy combined with radiotherapy on the immune environment of CRC.