Immunotherapy-induced microsatellite instability status shift in recurrent perihilar cholangiocarcinoma: A case report.

Immunotherapy revolutionized the treatment of biliary tract tumors and tumors with high microsatellite instability (MSI-H). This paper reports a 52-year-old woman with recurrent perihilar cholangiocarcinoma. The tumor was initially microsatellite stable (MSS) and proficient mismatch repair (pMMR) but shifted to MSI-H and deficient mismatch repair (dMMR) after combined immunotherapy. Following laparoscopic radical resection for jaundice, stage IV recurrence was diagnosed. Genetic testing revealed the MSS status. Subsequent treatment with camrelizumab and lenvatinib led to a partial response. Ovarian metastases, removed due to abdominal symptoms, exhibited dMMR and MSI-H. The mismatch in MSI status between the primary tumor and metastases suggests tumor heterogeneity and the influence of spatial or temporal factors. This shift can have important clinical significance since MSI-H is associated with significant responses to immune checkpoint inhibitors. MSI-H should be systematically tested in tumors and metastases to personalize treatments. MSI heterogeneity is not only rare but potentially has implications for treatment personalization and prognosis in patients with cholangiocarcinoma. This case highlights the dynamic changes in tumor characteristics during immunotherapy.