Circulating tumor DNA (ctDNA) is a powerful tool in bladder cancer. A positive result post-surgery is a strong indicator for initiating adjuvant therapy. However, a negative result does not guarantee a cure, as a notable percentage of these patients still relapse, making clinicians cautious about withholding treatment based on a single negative test.

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.

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.

In early-stage non-small cell lung cancer, the presence of circulating tumor DNA before surgery is not a statistically significant predictor of survival. However, detecting ctDNA after curative-intent surgery is a strong negative prognostic indicator, highlighting the critical value of post-operative testing.

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.

In the LAURA trial, 56% of patients remained MRD-positive after definitive chemoradiation. This indicates that local therapy is often insufficient to eradicate the disease, suggesting early micrometastasis is common and providing a strong rationale for consolidation therapy.

In neoadjuvant breast cancer treatment, patients with residual cancer post-therapy remain at high risk of recurrence (10-20%) even if their ctDNA tests are negative. This finding suggests that the physical presence of residual disease is a critical factor, and ctDNA status alone cannot justify forgoing additional adjuvant therapy in this cohort.

Experts warn against over-interpreting a single negative ctDNA test after surgery, clarifying that these patients still face a significant 25-30% risk of recurrence. The biomarker's true prognostic power comes from serial testing that shows a patient remains persistently negative over time.