Circulating tumour DNA (ctDNA) is transforming how we diagnose and treat complex cancers, particularly when clinical pathways are constrained by the speed, safety, and limitations of tissue biopsy.
The traditional diagnostic route can be prolonged and invasive, and may not be suitable for patients who are unwell. In advanced disease, this can lead to fewer treatment options and poorer outcomes.
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CtDNA liquid biopsy testing helps close this gap. By analysing tumour-derived DNA fragments shed into the bloodstream, we can gain actionable molecular information from a simple blood sample, supporting precise clinical decisions and personalised care.
One of the most meaningful impacts of ctDNA testing is providing patients with a faster diagnosis. For example, in suspected lung cancer, patients may be waiting for a bronchoscopy or a CT-guided biopsy, or be too unwell to undergo invasive procedures. Even when tissue is obtained, small lung biopsies commonly leave insufficient material for comprehensive tumour profiling. CtDNA testing can offer faster molecular diagnosis, allowing patients to start targeted treatment sooner and thereby improving outcomes.
I recall a patient who presented with breathlessness, and his imaging was highly suggestive of advanced lung cancer. He also had a severe chest infection, required high-flow oxygen, antibiotics, and was not fit for biopsy. A ctDNA test identified an easily targetable EGFR mutation, enabling therapy to be started promptly. Within two weeks, he was discharged, demonstrating how ctDNA testing can improve the time to diagnosis and treatment.
The same principle applies when tissue biopsies are difficult or dangerous to obtain, such as pancreatic and bile duct cancers, lesions close to major vessels, and cancers of unknown primary. In these settings, ctDNA testing can help avoid a prolonged diagnostic process and support earlier, molecularly matched treatment decisions.
CtDNA is also invaluable for treatment selection in relapsed or metastatic disease, as it can molecularly match patients to targeted therapies rather than having a “one-size-fits-all” approach. In ER-positive metastatic breast cancer progressing on endocrine treatment, identification of resistance mutations such as ESR1 and targetable changes like PIK3CA can guide treatment decisions. This is also particularly helpful in patients with bone-only metastases, where bone biopsies are too painful, and in heterogeneous disease, where a single lesion may not represent the full molecular profile.
CtDNA can also identify patients who are at risk of toxicity, and for some, this is the fastest and sometimes only route to getting the right diagnosis and a truly personalised treatment plan.
At The Royal Marsden, the Marsden360 test offers comprehensive ctDNA liquid biopsy testing and genomic profiling. Our world-leading experts who make up our molecular tumour board can support clinicians in interpreting complex results, and we routinely return results within 10 days, significantly shortening the diagnostic pathway, supporting earlier, more confident treatment decisions, and improving patient outcomes.
We owe it to every patient to offer them the best possible treatment for them and their cancer, and I believe that comprehensive genomic testing is one of the most reliable and fastest ways to achieve this. To learn more, visit the Marsden360 video FAQ hub or contact us today.
