Exceptional Response to Pembrolizumab Following Durvalumab Failure in a Patient With Microsatellite Instability-High Cholangiocarcinoma.

Typically, patients with advanced cholangiocarcinoma have a poor prognosis because of the limited effective chemotherapy options available. Studies on genotype-directed therapies for cholangiocarcinoma are increasing. However, limited clinical data are currently available for evaluating the efficacy of molecular-targeted therapies. Herein, we report the case of an 83-year-old man diagnosed with microsatellite instability-high (MSI-H) cholangiocarcinoma. MSI-H was detected using comprehensive genomic profiling after resistance to chemotherapy with durvalumab, an anti-programmed death ligand-1 (anti-PD-L1) antibody. Subsequently, the patient received pembrolizumab, a humanized IgG4 monoclonal antibody that targets anti-programmed cell death protein-1 (anti-PD-1). A CT scan after four cycles of pembrolizumab revealed marked shrinkage of the primary tumor. He experienced grade 2 cutaneous immune-related adverse events, but these events improved with topical steroid treatment. The patient is currently being treated with pembrolizumab for at least 10 months and has not exhibited any tumor (A1) progression. To the best of our knowledge, this is the first report on the efficacy of treatment with an anti-PD-1 antibody in a patient with MSI-H cholangiocarcinoma after the failure of the anti-PD-L1 antibody treatment.