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While microRNA-371 is a promising biomarker, it is not expressed in teratomas. Tissue-informed circulating tumor DNA (ctDNA) has shown an ability to detect teratoma in post-chemotherapy residual masses. This gives ctDNA a distinct advantage in this specific clinical scenario, potentially helping patients avoid major surgery.
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For extrahepatic cholangiocarcinoma, obtaining a sufficient tissue sample for diagnosis and molecular profiling can be extremely difficult. Circulating tumor DNA (ctDNA) testing, or liquid biopsy, serves as a crucial alternative in these cases, providing a non-invasive method to secure a diagnosis and identify actionable mutations when a traditional tissue biopsy is not feasible.
A key conceptual shift is viewing ctDNA not as a statistical risk marker, but as direct detection of molecular residual disease (MRD). This framing, similar to how a CT scan identifies metastases, explains its high positive predictive value and justifies its use in making critical treatment decisions.
ctDNA testing (liquid biopsy) is more effective than tissue biopsy for identifying ESR1 mutations. It samples DNA from all metastatic sites, capturing the disease's genetic heterogeneity and reflecting the most active resistance mechanisms, unlike a single-site needle biopsy which can miss them.
The original Signatera assay used 16 personalized probes based on whole-exome sequencing to find ctDNA. The next-generation version, based on whole-genome sequencing, expands this to 64 probes. This is expected to significantly increase sensitivity, detect molecular relapse earlier, and provide a longer window for clinical intervention.
After immunotherapy, many colorectal cancer patients have residual nodules on scans that appear to be partial responses. However, ctDNA testing can confirm these are often just scar tissue, not active disease. This provides the confidence to stop therapy at the two-year mark and avoid unnecessary surgeries for what are effectively complete responses.
Circulating tumor DNA (ctDNA) analysis allows for early detection of resistance mechanisms, such as secondary FGFR2 mutations, before tumors show growth on scans. This provides a potential window to adjust treatment strategies proactively, offering an advantage over traditional imaging-based monitoring.
For MSI-high patients responding to immunotherapy, a lingering mass on a CT scan may not be active cancer. A negative ctDNA test can help confirm that the visible lesion is likely just scar tissue, potentially averting unnecessary surgery.
A study where celecoxib initially failed to show benefit was re-analyzed using ctDNA. The drug provided a substantial survival improvement (HR 0.55-0.58) specifically in ctDNA-positive patients. This demonstrates ctDNA's power not just for prognosis, but as a predictive biomarker to identify which patients will benefit from a targeted therapy.
ctDNA testing does more than identify targetable mutations. The mutant allele fraction provides a quasi-volumetric measure of tumor burden, and its early clearance on therapy (as seen in MONALEESA-3) is a strong prognostic indicator for survival, adding value beyond standard radiographic assessment.
Hematologic cancers often have a single, common genetic marker per disease, enabling MRD detection with simple PCR for decades. Solid tumors are genetically diverse, lacking a universal marker. This required developing personalized, multi-probe assays like Signatera to track unique mutations, explaining the field's more recent progress.