To evaluate whether inosine can enhance the efficacy of immunotherapy in metastatic colorectal cancer in clinical treatment.

This study reviewed the data of patients with microsatellite-stabilized/proficient mismatch repair with metastatic colorectal cancer who were seen at Beijing Friendship Hospital, Capital Medical University from December 2020 to January 2023 and whose treatment regimen was fruquintinib/regorafenib +camrelizumab for injection. Patients were categorized into the inosine and the non-inosine groups according to whether they were combined with the application of inosine or not. The primary observational endpoint was objective response rate (ORR), and the secondary observational endpoints were overall survival (OS)and progression-free survival (PFS), and disease control rate (DCR).

A total of 36 patients were included, eighteen in the inosine group and eighteen in the non-inosine group. The median PFS in the inosine group was 3.10 months (95%CI: 2.823~3.377), and was 2.00 months (95%CI: 1.030~2.970) in the non-inosine group, there were significant differences between the two groups(χ²=4.539, P=0.033; HR=0.49, 95%CI: 0.246~0.965); the median OS was 17.47 months (95%CI: 3.046~31.887) in the inosine group, and was 11.23 months (95%CI:8.889~13.577)in the non-inosine group, there were significant differences between the two groups (χ²=10.025, P=0.002; HR=0.27, 95%CI: 0.111~0.638). The ORR and the DCR tended to be higher in the inosine group than in the non-inosine group, but with no statistical difference(P>0.05).In the subgroup analysis, in the <65-year-old group, the median OS in the inosine group was prolonged by 7.24 months, and the DCR was increased 50.0% in the inosine group; in the ≥65-year-old group, the median PFS in the inosine group was prolonged by 2.33 months, and the median OS in the inosine group was prolonged by 8.13 months; in the group with a platelet-to-lymphocyte ratio(PLR) <229, the median OS in the inosine group was prolonged by 10.87 months; in the group with a PLR ≥229, the median PFS in the inosine group was prolonged by 2.03 months and the median OS was prolonged by 3.77 months; the differences were statistically significant (P<0.05).

The median PFS and OS were prolonged in the inosine group compared with the non-inosine group in this trial, and inosine could enhance the immune checkpoint inhibitor effect of microsatellite stability/proficient mismatch repair metastatic colorectal cancer.