Cancer Dictionary · Gastrointestinal

Biliary Tract Cancer

Biliary tract cancers are grouped together but differ substantially by site. Intrahepatic cholangiocarcinoma in particular has a high frequency of actionable alterations, including FGFR2 fusions and IDH1 mutations. This is a disease where profiling is worth doing early rather than after other options are exhausted.

Also called Cholangiocarcinoma, Gallbladder cancer, Bile duct cancer.

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The governing idea

Biliary tract cancer is the uncommon disease with an unusually high rate of actionable findings, which makes comprehensive profiling more consequential here than its rarity would suggest.

01Before any molecular question

How it usually presents

Usually established first: the anatomical site (intrahepatic, perihilar, distal bile duct or gallbladder), stage, resectability, and whether biliary drainage is required. The site matters molecularly as well as surgically, because the alteration frequencies differ.

Usually already established

Anatomical site
Stage and resectability
Whether biliary drainage has been established
Whether the diagnosis was incidental after cholecystectomy

Major disease categories

The divisions below are not labels. Each one changes what the treatment discussion is actually about.

Intrahepatic cholangiocarcinoma

The site with the highest frequency of actionable findings, particularly FGFR2 fusions and IDH1 mutations.

Perihilar cholangiocarcinoma

Anatomically complex, with drainage and resectability dominating early management.

Distal cholangiocarcinoma

Managed surgically in a way that overlaps with pancreatic head tumours.

Gallbladder cancer

A distinct molecular profile, with ERBB2 alterations more prominent. Frequently found incidentally after gallbladder surgery.

03What is discussed

Molecular considerations

FGFR2 fusions and IDH1 mutations are the two findings most associated with intrahepatic cholangiocarcinoma, and both have dedicated targeted classes. ERBB2 amplification and mutation are more frequent in gallbladder cancer and distal disease. BRAF V600E, NTRK fusions, RET fusions, mismatch repair deficiency and BRCA alterations are all seen at lower frequency. Collectively, a substantial proportion of biliary tract cancers carry something actionable, which is a higher rate than in most gastrointestinal cancers. Because FGFR2 findings are fusions, the panel must read structural rearrangements to detect them.

Biomarkers commonly discussed

FGFR2

Fusions specifically, and mainly in intrahepatic disease. Requires a fusion-capable panel.

IDH1

Mutations, mainly in intrahepatic disease, with a dedicated targeted class.

ERBB2 (HER2)

More prominent in gallbladder and distal bile duct cancer.

BRAF

V600E specifically.

MMR / MSI

Uncommon, but changes the discussion where present.

NTRK and RET

Rare fusions, actionable across tumour types.

BRCA1 and BRCA2

Seen at low frequency, and raise a germline question.

This is not an exhaustive list, and which markers are relevant depends on the individual case. Not every marker listed is assessed in every patient.

04What is tested, and from what

Testing, inherited risk and blood-based monitoring

Genomic testing considerations

Comprehensive profiling that includes fusions is worth arranging early in advanced biliary tract cancer, because the rate of actionable findings is high and several of the key findings are structural. Tissue is often limited, coming from a biopsy of a difficult-to-reach lesion, so plasma testing is a common complement. The anatomical site should be stated clearly, because it changes what is most likely to be found.

Germline considerations

BRCA and other DNA repair alterations are found at low frequency and raise a germline question. Lynch syndrome is also relevant. Germline testing is not universal here in the way it is for pancreatic or ovarian cancer, but a suggestive family history or a relevant tumour finding is a reasonable prompt.

Cancer genetics and hereditary risk

ctDNA and liquid biopsy considerations

Plasma testing is commonly used where tissue is limited, which is frequent in this disease. It is also used at progression, particularly to look for acquired resistance alterations in FGFR2, which are a well-described mechanism.

When molecular information matters

Testing that arrives after the decision it was meant to inform has already been made is a common and avoidable problem. This is the sequence in which molecular information tends to become relevant.

At diagnosis of advanced diseaseComprehensive profiling including fusions is worth arranging early, given the high rate of actionable findings.
Where tissue is limitedPlasma testing in parallel avoids losing weeks to a failed tissue attempt.
At progression on a targeted agentRepeat profiling is discussed, particularly for acquired FGFR2 resistance alterations.
After incidental gallbladder cancerWhere cancer is found unexpectedly after routine surgery, staging and profiling decisions follow quickly.

06Take these to your team

Questions worth raising

When a decision is being made

Questions worth raising with a treating team.

Has comprehensive profiling that reads fusions been arranged, since FGFR2 fusions cannot be detected otherwise?
Has the anatomical site been stated, since it changes what is most likely to be found?
Is profiling being done early rather than after other options are exhausted, given the high rate of actionable findings?
Has HER2 been assessed, particularly in gallbladder and distal disease?

At progression, recurrence or resistance

The molecular picture at diagnosis is not always the molecular picture later.

Has repeat profiling been done at progression on a targeted agent, particularly to look for acquired FGFR2 alterations?
Has plasma been used at progression, given how well described resistance mutations are in this disease?

07What shapes eligibility

Clinical trial considerations

Biliary tract cancer has an active trial landscape organised around FGFR2, IDH1, HER2 and other specific alterations. Molecular eligibility is usually precise, so an incomplete profile is a common reason a patient cannot be assessed.

Ask about trial matching

Plain-language glossary for this entry (4 terms)

Term	What it means
Intrahepatic	Arising from bile ducts inside the liver. The site with the most actionable findings.
Perihilar	Arising where the bile ducts leave the liver. Anatomically complex.
Incidental gallbladder cancer	Cancer found unexpectedly in a gallbladder removed for other reasons.
Biliary drainage	Relieving a blocked bile duct. Often needed before treatment can start.

Where OnKommon fits

These are the services most often relevant to this cancer. Which of them applies is a clinical question, not an automatic one.

Signature STb O+The 523-gene comprehensive panel, with TMB and MSI.See how it works Signature STt OProfiling from an existing FFPE tissue block.See how it works SentinelSerial monitoring during active treatment.See how it works DecipherReinterprets sequencing already done elsewhere, without repeating it.See how it works

This entry is educational. It describes what is commonly discussed in this cancer, not what should happen for any individual. Which of it applies depends on the specific diagnosis, stage, prior treatment and the person themselves. Nothing here is a recommendation, and no list of biomarkers here is exhaustive. Decisions belong with a treating team who know the whole case.

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