The platform used for detecting ctDNA was not sensitive enough.

Circulating tumor DNA assays are becoming relevant for routine diagnostics, but many related aspects are yet unresolved. With this project, the investigators aim to develop pragmatic molecular diagnostic pathways of liquid biopsies relevant in advanced gastrointestinal malignancies with focus on clinical utility and sensible use of resources. They want to evaluate the ctDNA assays on a fully automated "low-cost" multiplex platform which is already implemented in routine molecular diagnostics of solid biopsies. The project will evaluate to what extent these ctDNA assays are relevant for clinical decision-making.

Advanced pancreatic cancer (PDAC) and cholangiocarcinoma (CCA): -Could the Idylla ctKRAS test select the ~10% of PDAC patients with KRASwt eligible for more extensive diagnostics? In PDAC and CCA, is it possible to detect patient samples with KRAS G12C or BRAF mutation for study inclusion? Could the ΔCq-value of the tests be used as a semi-quantitative tumor marker? What is the clinical value compared to the current tumor marker CA19-9?

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Metastatic Colorectal Cancer: Are the ctDNA assays useful in detecting primary resistance and/or monitoring for secondary/acquired resistance to EGFR antibody treatment? How does the sensitivity, specificity and turnaround time of the ctDNA assays compare to tissue-based analysis? Could the Idylla ctDNA assays accelerate detection of KRAS G12C or BRAF mutations, and hence facilitate study inclusion in the first line setting? Could the ctDNA assays guide rechallenge with EGFR treatment?

Can the information of liver metastases or prognostic markers (s-CEA, s-CRP) guide timing of ctDNA sampling?

Inclusion Criteria:

Newly referred patients with advanced pancreatic cancer (~20/year), Cholangiocarcinoma (~20/year), metastatic colorectal cancer (mCRC) (~50/year) and anti-EGFR-treated mCRC patients (~10/year) to Oslo University Hospital are eligible for inclusion.

Advanced malignancy