Effective Response of Intrahepatic Cholangiocarcinoma to Pembrolizumab: A Case Report.

Background/aim The efficacy of pembrolizumab for intrahepatic cholangiocellular carcinoma (IHCCC) is not widely reported. Case report We began pembrolizumab treatment in a 69-year-old male with recurrent IHCCC at 18 months after his surgery because of the proven microsatellite instability (MSI)-high status. The patient had partial response, with an 82.5% reduction at the end of 18 courses. Immunostaining of the primary tumor revealed intra-tumoral infiltration of both PD-1+ and CD8+ T cells, and a low expression of PD-L1. Conclusion Intra-tumoral infiltration of both PD-1+ and CD8+ T cells may be a predictive factor of the efficacy of pembrolizumab. Expression of PD-L1 did not correlate with a therapeutic effect, but the tumor microenvironment of our patient's recurrent lesions may have been modified by conventional chemotherapy and CD8+ T cells.