A study switching therapy based on ctDNA-detected ESR1 mutations revealed patients felt significantly better after the switch, even without visible tumor progression on scans. This counterintuitive finding suggests molecular progression has a subclinical impact on quality of life, supporting proactive, biomarker-driven treatment changes before patients clinically deteriorate.

An expert oncologist advises against ordering ctDNA tests that merely provide a "good or a bad feeling" about prognosis. The most valuable use is when a positive or negative result clearly dictates a clinical action, such as when to stop or restart adjuvant therapy.

Dr. Pusztai clarifies the ctDNA lexicon: "Molecular relapse" is when a supposedly cured patient turns ctDNA positive during surveillance. "Molecular progression" is when a metastatic patient on therapy develops new resistance mutations detectable in ctDNA before clinical progression. This specific terminology is key for precise clinical decision-making.

Emerging data from major trials shows that ctDNA clearance during neoadjuvant therapy and negative post-surgical MRD status are strong predictors of improved survival. MRD positivity, in contrast, is associated with worse biology and rapid progression.

Data from the ADAURA trial suggests that EGFR-mutated lung cancer patients with detectable ctDNA before starting adjuvant osimertinib are at very high risk of recurrence. This finding supports considering indefinite, lifelong osimertinib for this subgroup, deviating from the standard three-year duration.

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.

The InVigor11 study was the first to show that detecting recurrence via a ctDNA test before it's visible on scans is not just a prognostic sign, but an actionable clinical state. Intervening with therapy at this early stage was proven to improve patient outcomes, establishing a new paradigm for cancer surveillance.

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.

The main barrier to widespread ctDNA use is not its proven ability to predict who will recur (prognostic value). The challenge is the emerging, but not yet definitive, data on its ability to predict a patient's response to a specific therapy (predictive value).