Colorectal cancer, radiotherapy and gut microbiota.

Colorectal cancer is closely related to inflammation and immune response. Radiotherapy, as a major treatment for colorectal cancer, plays a central role in cancer control. Inflammation caused by ionizing radiation can exert either anti- or pro-tumorigenic effects. Additionally, radiotherapy can elicit an anti-tumor response not only in radiation of target lesions but also in radiation of remote lesions. However, the immune mechanism underlying this effect has not been thoroughly elucidated yet. The combination therapeutic regimen of radiotherapy with other therapeutic methods, including chemotherapy and immunotherapy, has been applied in clinical practice. Meanwhile, radiation toxicity and radiosensitivity have long been problems that affect a patient's quality of life and morbidity. Researchers have found that the abovementioned problems are closely associated with gut microbiota. Here we discuss the impact of immune response induced by radiotherapy on tumor regression and the impact of intestinal flora on the consequent clinical efficacy.