Pathological Complete Response after Pembrolizumab Treatment for Unresectable Perihilar Cholangiocarcinoma with High Microsatellite Instability: A Case Report

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INTRODUCTION: Pembrolizumab has been introduced to solid cancers with microsatellite instability (MSI)-high cases; however, its clinical experience for cholangiocarcinoma remains very limited. Here, we present a case who successfully underwent conversion surgery following pembrolizumab treatment for MSI-high perihilar cholangiocarcinoma, which pathologically exhibited complete response. CASE PRESENTATION: A 69-year-old male with Bismuth IV perihilar cholangiocarcinoma with bulky lymphadenopathy was referred, who initially required left hepatic trisectionectomy, caudate lobectomy, bile duct resection, and portal vein resection and reconstruction (H123458-B-PV). During the waiting period after preoperative portal vein embolization, the right hepatic artery was involved by rapid tumor progression, needing a modification of the initially scheduled surgical procedure to additional hepatic artery resection and reconstruction (H123458-B-PV-HA). We revised the surgical decision of resectable to locally unresectable disease. He received systemic chemotherapy with gemcitabine and cisplatin as first-line, showing the best effect of stable disease followed by slight tumor progression and re-elevation of tumor marker after 5 courses of treatment. Cancer multi-gene panel analysis using percutaneous biopsy specimen showed the nature of MSI-high. Therefore, he received pembrolizumab treatment as second-line therapy, leading to a drastic downsize >30% in tumor diameter and normalization of the tumor marker as well after only 2 cycles of administration. After confirmation of keeping tumor shrinkage during 22 courses of pembrolizumab treatment without any severe adverse events, we decided to perform conversion surgery and performed left trisectionectomy, caudate lobectomy, and bile duct resection with portal vein resection (H123458-B-PV). Although the right hepatic artery was extensively fibrotic, there was no evidence of malignancy by frozen section histologic diagnosis. The pathological findings showed pathological complete response with no residual tumor cells. The patient is under periodical checkup without adjuvant chemotherapy, and no tumor recurrence was observed at 4 months postoperatively. CONCLUSIONS: We experienced clinical partial response but pathological complete response after second-line pembrolizumab treatment for unresectable locally advanced perihilar cholangiocarcinoma with a biologic nature of MSI-high. Conversion surgery may be considered as a promising option for such effective case, whereas there is a possibility to avoid resection in the MSI-high setting.

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