Success rate of microsatellite instability examination and complete response with pembrolizumab in biliary tract cancer.

ABSTRACT

BACKGROUND AND AIM: The success rate of microsatellite instability (MSI) examination in biliary tract cancer (BTC) and the treatment outcomes of pembrolizumab in patients with MSI-high (MSI-H) BTC have not been fully investigated. We examined the success rate of MSI examination and the rate of MSI-H status in patients with BTC as well as the treatment outcomes of patients with MSI-H status who underwent pembrolizumab treatment. METHODS: We retrospectively reviewed 60 consecutive patients with unresectable or postoperative recurrent BTC who underwent MSI examination in a Japanese cancer referral center between January 2019 and September 2020. RESULTS: The study included 24 intrahepatic cholangiocarcinomas, 12 hilar cholangiocarcinomas, 4 distal cholangiocarcinomas, 16 gallbladder carcinomas, and 4 ampullary carcinomas. The methods of cancer tissue sampling were percutaneous liver tumor biopsy in 26 cases, surgery in 15 cases, endoscopic ultrasound fine-needle aspiration in 12 cases, transpapillary bile duct biopsy in 5 cases, and others in 2 cases. The success rate of MSI examination was 98.3% (59 of 60). MSI examination failed in only one case using a surgical specimen due to time-dependent degradation of DNA. The frequency of MSI-H BTC was 3.3% (2 of 60 cases). One patient with MSI-H intrahepatic cholangiocarcinoma achieved a complete response with pembrolizumab treatment. CONCLUSIONS: MSI examinations in BTC were successful in almost all cases, regardless of tissue sampling methods. We experienced a case in which pembrolizumab resulted in a complete response to MSI-H BTC. Since pembrolizumab for MSI-H BTC could prolong survival time, MSI examination should be performed proactively to increase treatment options.