Does pembrolizumab (Keytruda) work in biliary (bile duct) cancer?

Does Keytruda Work in Bile Cancer?

Yes, pembrolizumab (Keytruda) works in biliary tract cancer when combined with gemcitabine and cisplatin as first-line therapy, providing a statistically significant and clinically meaningful survival benefit, and it is FDA-approved for this indication. 1

First-Line Treatment: The Standard Approach

Pembrolizumab combined with gemcitabine and cisplatin should be considered standard of care for first-line treatment of unresectable or metastatic biliary tract cancer. 2, 3 This recommendation is based on the KEYNOTE-966 trial, which demonstrated:

• Median overall survival: 12.7 months with pembrolizumab plus chemotherapy versus 10.9 months with chemotherapy alone (HR 0.83, p=0.0034) 4
• The survival benefit was clinically meaningful, extending life by approximately 2 months
• No new safety signals compared to chemotherapy alone 4
• Grade 3-5 treatment-related adverse events occurred in 70% of pembrolizumab patients versus 69% in placebo group 4

The EASL 2025 guidelines specifically endorse this combination for extrahepatic cholangiocarcinoma, noting that gemcitabine and cisplatin with either durvalumab or pembrolizumab should be considered standard of care. 3

Important Nuance on Tumor Location

The benefit appears primarily driven by intrahepatic cholangiocarcinoma (HR 0.76), while the extrahepatic cholangiocarcinoma subgroup showed no clear benefit (HR 0.99) in KEYNOTE-966. 3 However, the overall population benefit and FDA approval support its use across all biliary tract cancers.

Biomarker-Selected Populations: When Pembrolizumab Works Best

MSI-H/dMMR Tumors (Strongest Response)

For patients with MSI-H or dMMR biliary tract cancer, pembrolizumab monotherapy is highly effective and FDA-approved. 1 The KEYNOTE-158 trial data showed:

• Overall response rate: 40.9% in cholangiocarcinoma/biliary tract subgroup 2
• Median overall survival: 19.4-24.3 months 2
• Median duration of response: 47.5 months in the broader MSI-H cohort 2
• Only 12% experienced grade 3-5 treatment-related adverse events 2

Pembrolizumab is recommended as useful-in-certain-circumstances for first-line or subsequent-line therapy in MSI-H/dMMR biliary tract cancers, though data in the first-line setting are limited. 2

TMB-High Tumors (Subsequent-Line Only)

For TMB-H tumors (≥10 mutations/megabase), pembrolizumab is FDA-approved for subsequent-line therapy only after progression on prior treatment. 2, 1 Key points:

• Response rate: 29% in TMB-H tumors across solid tumors 2
• Approximately 4% of advanced biliary tract cancers are TMB-H 2
• None of the 63 biliary tract cancer patients in KEYNOTE-158 TMB cohort were TMB-H, but other studies support testing 2
• NCCN recommends this as useful-in-certain-circumstances for subsequent-line therapy only 2

Unselected Populations (Lower Response)

In patients without MSI-H, dMMR, or TMB-H status, pembrolizumab monotherapy has limited activity:

• Overall response rate: 5.8-13% in KEYNOTE-158 and KEYNOTE-028 studies 5
• Median overall survival: 5.7-7.4 months 5
• PD-L1 expression did not predict response (6.6% ORR in PD-L1+ vs 2.9% in PD-L1-) 5
• Responses were durable when they occurred (median duration not reached) 5

Clinical Algorithm for Using Pembrolizumab in Biliary Tract Cancer

Step 1: Determine disease stage and prior treatment

• If newly diagnosed unresectable/metastatic → Consider first-line pembrolizumab + gemcitabine + cisplatin
• If previously treated → Test for biomarkers before selecting pembrolizumab

Step 2: Test for predictive biomarkers

• MSI-H/dMMR status (FDA-approved test required) - highest priority
• TMB status (if MSI-H/dMMR negative and considering subsequent-line therapy)
• PD-L1 testing is NOT required for first-line combination therapy

Step 3: Select appropriate regimen

• MSI-H/dMMR positive: Pembrolizumab monotherapy (any line, no prior checkpoint inhibitor)
• TMB-H positive: Pembrolizumab monotherapy (subsequent-line only)
• Biomarker negative or unknown: Pembrolizumab + gemcitabine + cisplatin (first-line only)

Step 4: Duration of treatment

• Pembrolizumab: Maximum 35 cycles (approximately 2 years) 1
• Gemcitabine: Continue as maintenance (no maximum duration) 4
• Cisplatin: Maximum 8 cycles 4

Critical Pitfalls to Avoid

1. Do not use pembrolizumab monotherapy in unselected patients - The response rate is only 6-13% without biomarker selection 5

2. Do not skip biomarker testing in previously treated patients - MSI-H/dMMR patients have 40.9% response rates versus 5.8% in unselected populations 2, 5

3. Do not use TMB-H as a first-line indication - FDA approval and NCCN guidelines restrict this to subsequent-line therapy only 2

4. Do not assume PD-L1 predicts response - Studies show no correlation between PD-L1 expression and pembrolizumab efficacy in biliary tract cancer 6, 5

5. Do not continue cisplatin beyond 8 cycles - The protocol limits cisplatin to 8 cycles while continuing gemcitabine and pembrolizumab 4

Evidence Quality and Strength

The recommendation for first-line pembrolizumab + chemotherapy is based on Level 2 evidence with strong consensus from the most recent 2025 NCCN guidelines 2 and 2025 EASL guidelines 3, supported by the phase 3 KEYNOTE-966 trial 4. The MSI-H/dMMR indication has FDA approval based on the KEYNOTE-158 trial 1, though NCCN notes data are limited particularly in first-line settings 2.

The survival benefit, while statistically significant, represents a modest absolute improvement of approximately 2 months 4, which some may consider inadequate 7. However, this represents the best available evidence for improving mortality in this difficult-to-treat cancer.