In cholangiocarcinoma, when is immunotherapy indicated, which biomarkers (MSI/dMMR, tumor‑mutational burden) should be tested, and what are the recommended immunotherapy regimens?

Immunotherapy for Cholangiocarcinoma

First-Line Treatment: Immunotherapy Combined with Chemotherapy

For patients with advanced/unresectable cholangiocarcinoma and good performance status (ECOG 0-1), gemcitabine plus cisplatin combined with durvalumab or pembrolizumab is the standard first-line treatment, regardless of MSI status. 1, 2, 3 This recommendation is based on the TOPAZ-1 trial, which demonstrated improved overall survival (12.8 vs 11.5 months; HR 0.80; p=0.021) with the addition of durvalumab to chemotherapy. 2, 3

• The French Association for the Study of the Liver (AFEF) provides a Grade 2+ recommendation with strong agreement for adding durvalumab or pembrolizumab to 6-month cisplatin-gemcitabine regimen in patients with ECOG 0-1. 1
• Pembrolizumab is FDA-approved for biliary tract cancer (BTC) in combination with chemotherapy, administered at 200 mg every 3 weeks or 400 mg every 6 weeks, given prior to chemotherapy on the same day. 4

Biomarker Testing: What to Test and When

All patients with advanced cholangiocarcinoma should undergo comprehensive molecular profiling at first-line treatment initiation, including MSI/dMMR testing, TMB assessment, and evaluation for actionable mutations. 1

Required Biomarker Panel (Grade 1+ recommendation):

• MSI/dMMR status: Immunohistochemistry for MLH1, MSH2, MSH6, and PMS2 proteins, with confirmation by Pentaplex PCR if dMMR is detected. 1
• Tumor mutational burden (TMB): Next-generation sequencing coupling MSI and TMB analysis represents a decisive tool for selecting patients for immunotherapy. 1
• Additional molecular targets: HER2 (IHC with FISH confirmation if 2+ or 3+), IDH1, KRAS, BRAF mutations, and FGFR2/NTRK fusion transcripts via NGS-based RNA panel. 1

Testing Methodology:

• First-line approach: Immunohistochemistry for MMR proteins (MLH1, MSH2, MSH6, PMS2) with strong agreement from ESMO consensus. 1
• Second-line approach: PCR-based assessment using five microsatellite markers including at least BAT-25 and BAT-26. 1
• Comprehensive approach: NGS-based testing can simultaneously assess MSI, TMB, and actionable mutations in a single assay. 1

Immunotherapy Indications Based on MSI Status

MSI-High/dMMR Cholangiocarcinoma:

For MSI-H/dMMR cholangiocarcinoma, immune checkpoint blockade (pembrolizumab or dostarlimab) is strongly recommended after progression on first-line chemotherapy. 1, 2, 3

• Pembrolizumab demonstrated 53% objective response rate with 21% complete response in dMMR/MSI-H advanced cancers including cholangiocarcinoma. 2
• The AFEF guidelines provide Grade 2+ recommendation with strong agreement for pembrolizumab in MSI-H patients. 1
• International consensus guidelines (JSCO-ESMO-ASCO-JSMO-TOS) provide Level III evidence, Grade A recommendation with 100% agreement for PD-1/PD-L1 inhibitors in MSI/dMMR tumors. 2
• FDA approval exists for pembrolizumab as single-agent therapy for MSI-H/dMMR solid tumors, including cholangiocarcinoma. 4, 5

Dosing for MSI-H/dMMR: Pembrolizumab 200 mg every 3 weeks or 400 mg every 6 weeks until disease progression, unacceptable toxicity, or up to 24 months. 4

MSI-Low/Microsatellite Stable (MSS) Cholangiocarcinoma:

For MSI-low/MSS cholangiocarcinoma, single-agent immunotherapy is NOT recommended, as these tumors lack the high neoantigen burden required for immunotherapy response. 2

• First-line treatment remains gemcitabine-cisplatin plus durvalumab or pembrolizumab (combination therapy, not monotherapy). 2, 3
• After progression on first-line therapy, second-line options include FOLFOX chemotherapy, FGFR inhibitors (if FGFR2 fusions present), or ivosidenib (if IDH1 mutations present), but NOT immune checkpoint blockade monotherapy. 1, 2

TMB-High as Alternative Biomarker

In patients unable to undergo confirmatory MSI-H/dMMR testing, TMB ≥10 mutations/megabase (as determined by FDA-approved test) may be used to select patients for pembrolizumab monotherapy. 4

• This is particularly relevant when local MSI testing shows discordance with FDA-approved tests. 4
• NGS-based testing coupling MSI and TMB analysis received "very strong agreement" from ESMO consensus for selecting patients for immunotherapy. 1

Treatment Algorithm by Clinical Scenario

Scenario 1: Newly Diagnosed Advanced Cholangiocarcinoma (ECOG 0-1)

1. Obtain comprehensive molecular profiling including MSI/dMMR, TMB, FGFR2, IDH1, HER2, BRAF, NTRK. 1
2. Initiate gemcitabine-cisplatin plus durvalumab or pembrolizumab regardless of MSI status. 1, 2, 3
3. Continue until disease progression, unacceptable toxicity, or 24 months. 4

Scenario 2: Progression After First-Line Therapy (MSI-H/dMMR)

1. Switch to pembrolizumab monotherapy 200 mg every 3 weeks or 400 mg every 6 weeks. 1, 2, 4
2. Continue until disease progression, unacceptable toxicity, or 24 months. 4
3. Alternative: dostarlimab for MSI-H/dMMR disease. 1

Scenario 3: Progression After First-Line Therapy (MSI-Low/MSS)

1. FOLFOX chemotherapy (Grade 1+ recommendation). 1
2. If FGFR2 fusions/rearrangements: pemigatinib, futibatinib, or infigratinib (Grade 2+ recommendation). 1
3. If IDH1 mutations: ivosidenib (Grade 1+ recommendation). 1
4. If BRAF V600E: dabrafenib plus trametinib (Grade 2+ recommendation). 1
5. If HER2 amplification: trastuzumab plus pertuzumab or zanidatamab (Grade 2+ recommendation). 1
6. Do NOT use single-agent immunotherapy. 2

Scenario 4: Impaired Performance Status (ECOG 2)

1. Gemcitabine monotherapy (Grade 2+ recommendation). 1
2. Alternative: fluoropyrimidine alone. 1
3. Immunotherapy monotherapy is NOT recommended regardless of MSI status. 2

Scenario 5: Poor Performance Status (ECOG 3-4)

1. Supportive care only. 1
2. No active anticancer therapy recommended. 1

Critical Pitfalls to Avoid

Do not use single-agent immunotherapy in MSI-low/MSS cholangiocarcinoma, as these tumors lack sufficient neoantigen burden for response. 2 The combination of chemotherapy plus immunotherapy in first-line is appropriate, but monotherapy after progression is ineffective.

Do not delay molecular testing—obtain comprehensive profiling at diagnosis, not after first-line failure, as this guides both first-line combination therapy decisions and subsequent treatment options. 1

Do not assume MSI status remains stable—tumor heterogeneity can lead to MSI status shifts between primary tumor and metastases, or during treatment. 6 If feasible, retest metastatic sites, particularly if initial testing showed MSS but clinical response to immunotherapy is observed. 6

Do not rely solely on local MSI testing for treatment decisions—FDA recommends confirmation with FDA-approved tests due to discordance rates, or use TMB ≥10 mut/Mb as alternative selection criterion. 4

Do not treat patients with ECOG >2 with immunotherapy, as they derive no benefit and experience increased toxicity. 3

Emerging Considerations

Radiation therapy combined with immunotherapy may have synergistic effects in cholangiocarcinoma, particularly for oligometastatic disease. 3, 7 SBRT (30-50 Gy in 3-5 fractions) can be considered for unique intrahepatic lesions <5 cm during first-line immunotherapy-chemotherapy. 3 A case report demonstrated complete response with combined anti-PD-1 immunotherapy and radiotherapy in a patient with conflicting biomarker predictions. 7

PD-L1 expression and its relationship with MSI/TMB is complex and differs by tumor type. 1 While PD-L1 testing is not currently required for cholangiocarcinoma treatment decisions (unlike some other malignancies), the relationships between these biomarkers remain under investigation. 1