Efficacy of Combined PD-1 Inhibitor and Bevacizumab in Unresectable Liver Metastasis of MSI-H Colorectal Cancer: A Case Report.

BACKGROUND Programmed death 1 (PD-1) inhibitors have demonstrated limited effectiveness in patients with microsatellite instability-high (MSI-H) colorectal cancer (CRC). Recent studies suggest that their efficacy can be enhanced when combined with anti-angiogenic agents. CASE REPORT We present a case of a 25-year-old woman with CRC harboring a KRAS mutation and MSI-H status, along with initially unresectable liver metastases. Despite receiving first-line chemotherapy combined with bevacizumab, her disease progressed. Subsequently, she was treated with a combination of a PD-1 inhibitor and bevacizumab as second-line therapy. This approach resulted in a partial response, ultimately leading to a pathological complete response after resection of the liver metastases. The patient continued with the combination therapy for over a year and showed no serious treatment-related adverse events. Postoperative follow-up imaging confirmed the absence of tumor recurrence or metastasis, and the patient remained in remission. CONCLUSIONS This case highlights the potential of combining immune checkpoint inhibitors with anti-angiogenic agents in treating patients with MSI-H metastatic CRC, particularly those with initially unresectable liver metastases. Although further research is warranted to validate this therapeutic strategy, our findings support the use of this combination as a viable option for achieving pathological complete response and improving outcomes in this patient population. Comprehensive clinical studies are needed to optimize conversion therapy regimens and enhance the likelihood of success in treating patients with MSI-H CRC with advanced disease.