Background
Colorectal cancer, as a very common malignant tumor in the world, is always damaging people’s lives and properties. According to the cancer data just released at the beginning of 20241, as of 2022, colorectal cancer has the second highest incidence rate among all malignant tumors in the whole population, with the fourth highest incidence rate among women and the second highest incidence rate among men. The mortality rate was the fourth highest in the population as a whole. Therefore, it seems that colorectal cancer poses a huge health hazard to citizens, which should not be underestimated. In China, the 5-year survival rate of colorectal cancer patients is between 50% and 60%, which is slightly lower than that of the United States, Japan, and most European countries2,3,4. In addition, first-line treatment for metastatic colorectal cancer is effective, but benefit from back-line treatment remains limited5. At the same time, our country patients are mostly have good physical constitutions and have a higher likelihood of receiving back-line treatments6, making more appropriate treatments especially important for them. Around 2020, the advent of immunotherapy brought a new light to the treatment of malignant tumors. In particular, the discovery of immune checkpoint inhibitors, such as PD-L1 and CTLA-4, has been of great benefit to patients with malignant tumors in terms of prolonging survival time and improving their quality of life7,8. The combination of immunotherapy with conventional systemic chemotherapy has been particularly successful in lung cancer. However, in colorectal cancer patients, the efficacy of immunotherapy remains controversial due to issues such as its specific molecular mechanisms9. In particular, most experts have not reached a consensus on whether to combine immunotherapy in the back-line treatment of advanced colorectal cancer patients, the selection of immune checkpoint inhibitors of different pathways, or even the different types of immune checkpoint inhibitors at home and abroad. In addition, it is well known that immunotherapy is a therapeutic mode to inhibit immune escape and improve the tumor microenvironment to play an anti-tumor role. Therefore, many studies have confirmed that tumor microenvironment is particularly important for immunotherapy of tumors. However, for colorectal cancer, there are currently limited biomarkers that can predict disease outcome10.It has been shown that microsatellite status, TMB11, POLE/POLD1 mutation12, and PD-L1 expression13can assess the effectiveness of treatment with immune checkpoint inhibitors to varying degrees14,15,16.However, the factors sometimes fail to identify the dominant population that will ultimately benefit from immunotherapy due to individual differences and so on. Currently, there is an increasing number of research that suggests that inflammatory markers such as the degree of lymphocyte and neutrophil infiltration can largely predict the outcome of malignant tumors, especially immunotherapy, and the evidence for this claim is inextricably linked to the doctrine of the tumor microenvironment17.Thus, the inflammatory index in the patient’s body is closely related to the prognosis of colorectal cancer patients18. For patients with early-stage colorectal cancer, perioperative NLR may have a certain relationship with their recurrence and prognosis19. However, NLR have not received a great deal of attention and there is no uniformity for colorectal cancer patients in advanced stages, especially those receiving back-line immunotherapy. In this paper, through a retrospective case study, we analyzed that NLR in patients with treated advanced colorectal cancer can serve as an important predictor of the efficacy of immunotherapy, and at the same time confirmed the relationship between microsatellite status and the prognosis of immunotherapy, which further indicated that the degree of infiltration of inflammatory markers in the tumor microenvironment, such as lymphocytes and neutrophils, is closely related to the therapeutic efficacy of immune checkpoint inhibitors.