A case of perihilar cholangiocarcinoma with peritoneal dissemination that achieved a pathological complete response using immune checkpoint inhibitors: A case report.

Surgical resection is considered the only potentially curative treatment for biliary tract cancer (BTC). However, for patients with locally advanced or metastatic BTC, systemic chemotherapy remains the primary therapeutic option. Historically, chemotherapies such as gemcitabine plus cisplatin (GC), gemcitabine plus S-1, and GC plus S-1 have been employed; however, the prognosis remains poor. Recently, combined therapy with immune checkpoint inhibitors (ICIs) has emerged as a promising therapeutic approach for unresectable BTC. In cases with long-term efficacy to systemic chemotherapy, sequential surgical resection, known as conversion surgery, has also shown potential to improve overall outcomes in unresectable BTC. This case report presents a case of advanced perihilar cholangiocarcinoma with histologically confirmed peritoneal dissemination that achieved a pathological complete response after combination therapy with GC and durvalumab, followed by conversion surgery. Achieving a pathological complete response in the presence of peritoneal dissemination is rare. This case provides valuable insights into treatment strategies for this aggressive malignancy, demonstrating that a pathological complete response is possible even in the presence of peritoneal dissemination.