ideasIdea

Reflex HER2 testing of every advanced gallbladder and extrahepatic biliary cancer

Between one in eleven and one in five gallbladder cancers is HER2-positive and two HER2 drugs are now approved, but testing still happens only when someone asks. Making it automatic on every advanced biliary diagnosis, on resection tissue where it exists, would find the patients the trials were built for.

HER2 overexpression is about 20 percent in extrahepatic biliary cancers in the 2017 meta-analysis and 9.4 percent of gallbladder cancers by the HERIZON-BTC-01 definition in a 2026 resected series, which also found frequent heterogeneity involving under half of tumour cells, so small biopsies can miss it. Zanidatamab produced a 41.3 percent response rate in HER2-positive disease and trastuzumab deruxtecan has a tumour-agnostic HER2 3+ indication. Testing uptake in biliary cancer is not routinely audited. Reflex immunohistochemistry with in situ hybridisation for 2+ cases, ordered by pathology at diagnosis, is the model used for gastric and breast cancer.

Hypothesis

Pathology-initiated reflex HER2 testing at diagnosis of advanced gallbladder or extrahepatic biliary cancer will raise the tested fraction to above 90 percent and double the number of patients receiving HER2-directed therapy within two years.

Rationale

The drugs exist and are approved; the bottleneck is a test that is cheap, standardised and already run in every pathology laboratory for other cancers.

Proposed test

Before-and-after audit across a hepatobiliary network: proportion tested, turnaround time, HER2-positive rate, proportion of positives treated, with a heterogeneity sub-study comparing biopsy and resection specimens.

Maturity

early clinical

Who acts

clinic

Cost to try

Small (under $1M)

Years to first evidence

Bottlenecks it attacks

Biomarkers are not validated or standardised · Tests that decide who gets a drug are often not validated prospectively and are measured differently in every lab.
Knowledge reaches practice too slowly · Knowledge diffusion is slow: it takes years for a proven result to change what most patients receive, and no one can keep up with the literature.

Key papers

3top

observationalHuman Pathology 20260 citations

HER2 status in extrahepatic cholangiocarcinoma and gallbladder carcinoma: Concordance between immunohistochemistry and chromogenic in situ hybridization in 140 Cases

A lower, more conservative prevalence than the 2017 meta-analysis, using the trial's own definition. Heterogeneity means a small biopsy can miss HER2, which argues for testing resection specimens and for reflex testing rather than testing on request.

observationalThe Lancet Oncology 2023217 citations

Zanidatamab for HER2-amplified, unresectable, locally advanced or metastatic biliary tract cancer (HERIZON-BTC-01): a multicentre, single-arm, phase 2b study

One cancer page on OnCo cites this paper by its DOI; this record gives the citation a page of its own so a reader can follow it without leaving OnCo. Read the abstract above alongside the citing page listed under Related; the record was created automatically from the Europe PMC entry and its figures have not been checked by hand.

meta analysisCancer Metastasis Reviews 2017172 citations

HER2/HER3 pathway in biliary tract malignancies; systematic review and meta-analysis: a potential therapeutic target?

The prevalence estimate that made HER2 the first gallbladder-relevant target; it argues for testing every advanced gallbladder cancer, since one in five may qualify for zanidatamab or trastuzumab deruxtecan.