The REVEAL-BTC Study will analyze 5 biomarkes in samples of participants who in the past 15 year have been diagnosed with any stage of biliary tract cancer. The expression levels of the biomarkers will be correlated with clinical outcomes in the participants, which will lead to better patient stratification that will help guide the use of targeted therapies in the future.

In the REVEAL.BCT Study, archival tumor tissue samples available from multiple national sites in Spain will be collected alongside basic clinical and survival data of 244 participants. Then, samples will be evaluated for the expression of selected biomarkers (CLDN18.2, TROP2, B7-H4, HER2, and PD-L1) via immunohistochemistry. The main purpose of this analysis is to evaluate the expression levels of the biomarkers and understand its link to the participants' clinical outcome, with the aim to identify specific patient populations and strategies to help clinicians guide the use of targeted therapies in patients according to their markers in the future.

Inclusion Criteria:

1. Written informed consent for the use of clinical data and tissue samples is available. (The use of data and samples without consent is only possible if exemption is granted by the corresponding Institutional Review Board - IRB).
2. Histologically confirmed diagnosis of biliary tract cancer (including gallbladder carcinoma [GBC] or cholangiocarcinoma [CCA]), regardless of disease stage.
3. Diagnosis must have been established within the last 15 years prior to Study initiation.
4. Availability of archival formalin-fixed paraffin-embedded (FFPE) tumor tissue sample, collected prior to Study inclusion at any disease stage (e.g., during surgery or in the advanced setting). For patients with de novo metastatic disease or early stage primary tumors undergoing surgery, the tissue must have been obtained before the initiation of any systemic therapy (e.g. chemotherapy) or radiotherapy. For patients with recurrent disease undergoing a new biopsy, previous treatments are allowed.
5. Availability and accessibility of basic clinical information and survival data on medical records.

Exclusion Criteria:

1. Unavailability or inadequate quality (e.g., insufficient tumor content, degraded tissue) of archival FFPE tumor tissue samples for the planned immunohistochemical analysis.
2. Missing or incomplete basic clinical and/or survival data in the medical record.

Male and female participants with histologically confirmed biliary tract cancer (either GBC or CCA), regardless of disease stage, are eligible.

Participants must have been diagnosed within the past 15 years and must have archival tumor tissue available in the form of formalin-fixed-paraffin-embedded (FFPE) samples, collected prior to the start of the Study at any disease stage (e.g., during surgery of the primary or in the advanced setting).

Availability of basic clinical and survival data is required for Study participation. Confirmation of consent exemption must be obtained from the ethics committee at the time of submission.

Data collected within this study will be made available to researchers after contacting the corresponding author and upon revision and approval based on scientific merit by the trial management group (which includes a qualified statistician) of a detailed proposal for their use. The data required for the approved, specified purposes and the trial protocol will be provided after the completion of a data-sharing agreement that will be set up by the study sponsor. All data provided are anonymized to respect the privacy of patients who have participated in the trial in line with applicable laws and regulations. Data Sharing should begin 1 month after publication of study main results and ending 5 years after article publication. Estimate timeframe for response will be within 30 days.