Purpose: Standard-dose immune checkpoint inhibitors (SD-ICIs) are the standard of care as initial therapy in microsatellite instable-high (MSI-H) advanced/metastatic colorectal adenocarcinomas (mCRC), but there are preclinical data to suggest that low-dose ICIs (LD-ICI) might also have similar efficacy.
Materials and methods: A retrospective study of patients with MSI-H mCRC receiving ICIs between June 2017 and January 2023 was conducted. The primary end point of the study was 12-month progression-free survival (PFS), which was computed using the Kaplan-Meier method.
Results: A total of 65 patients were available for analysis during the study period. Sixty patients (92%) received nivolumab, whereas the remaining received pembrolizumab. First-line ICIs were received by 18 patients (28%), whereas 47 patients (72%) received ICIs during later lines. Thirty patients (47%) received LD-ICIs (all received nivolumab), with the remaining receiving SD-ICIs (53%). At a median follow-up of 16.5 (95% CI, 11.8 to 21.2) months, median PFS was not reached in the entire cohort. The 12-month PFS rate in the LD-ICI cohort was 90%, whereas it was 75.8% in the SD-ICI cohort. There were no statistical differences in patients receiving ICIs as first-line therapy (12 months PFS-94.4%) or during later lines of therapy (12-month PFS-77.9%; P = .56).
Conclusion: ICIs in the current study show survivals which are similar to those seen in seminal trials in patients with MSI-H mCRC. Low-dose ICIs appear to work in MSI-H mCRC and should be explored prospectively in clinical trials. Patients with MSI-H status should be exposed to ICIs, whether initially or later during treatment, whenever feasible.