Efficacy of Pembrolizumab as Conversion Therapy in Deficient Mismatch Repair/Microsatellite Instability-High Metastatic Liver Colorectal Cancer Associated With Lynch Syndrome: A Case-Based Analysis

Immunotherapy has emerged as a new standard of care for patients with unresectable or metastatic colorectal cancer characterized by microsatellite instability-high (MSI-H) or deficient mismatch repair (dMMR), owing to its superiority compared with conventional chemotherapy, as demonstrated in recent clinical trials. However, to date, no clinical trial has evaluated the role of immunotherapy as a neoadjuvant strategy aimed at converting potentially resectable hepatic metastases into candidates for curative surgery. In this report, we present the case of a patient with Lynch syndrome who developed hepatic metastasis after a right hemicolectomy for colon adenocarcinoma. The patient was treated with upfront pembrolizumab as conversion therapy following discussion in a multidisciplinary tumor board. After six cycles of immunotherapy, the patient had stable disease according to the Immune Response Evaluation Criteria in Solid Tumors (iRECIST), and a pathological complete response was achieved following complete resection of the liver metastasis.