# A Case of Pathological Complete Response after “Conversion Surgery” for Initially Unresectable Locally Advanced Intrahepatic Cholangiocarcinoma

## TL;DR

A patient with advanced liver cancer achieved complete remission after a combination of chemotherapy and an experimental drug, allowing successful surgery.

## Contribution

Reports a rare case of pathological complete response in intrahepatic cholangiocarcinoma following conversion surgery and combination therapy.

## Key findings

- A patient with initially unresectable iCCA became resectable after GCS chemotherapy and pembrolizumab.
- Post-surgery histopathology showed a pathological complete response with no recurrence after 5 years.
- MSI-H status and possible synergy between chemotherapy and pembrolizumab are suggested as contributing factors.

## Abstract

Intrahepatic cholangiocarcinoma (iCCA) is the second most common liver cancer and has a poor prognosis. Given the recent advancements in drug therapy, the topic of so-called “conversion surgery” in biliary tract cancer, including iCCA, is evolving; however, only a few cases have been reported.

A 50-year-old female was referred to our hospital for a liver tumor identified on abdominal ultrasonography. She was diagnosed with iCCA based on tumor biopsy. Due to extensive vascular and bile duct invasion, iCCA was initially considered unresectable. After 8 cycles of gemcitabine, cisplatin plus S-1 (GCS) therapy, CT revealed a partial response. Considering that microsatellite instability–high (MSI-H) was detected, we switched the regimen from GCS to pembrolizumab. However, after 1 cycle of pembrolizumab therapy, immune checkpoint inhibitor (ICI)–induced hepatitis was suspected; therefore, pembrolizumab therapy was suspended. GCS therapy was restarted, and after another 3 cycles, the iCCA was deemed resectable; therefore, conversion surgery was performed. Postoperative histopathological examination revealed a pathological complete response (pCR), and the patient remained alive more than 5 years postoperatively without recurrence or metastasis.

We experienced a case of pCR induced by GCS chemotherapy and pembrolizumab monotherapy. Although the direct contribution of pembrolizumab remains unclear, a possible synergistic effect with GCS chemotherapy was suggested, particularly in MSI-H tumors.