Not all ctDNA clearance is equal. Data from KEYNOTE-361 shows chemotherapy clears ctDNA more frequently (40%) but with poor correlation to outcomes. In contrast, immunotherapy clears ctDNA less often (11%), but those patients who do clear it experience brilliant, more durable outcomes, suggesting a different biological mechanism of response.

In patients achieving a complete response on EV-pembrolizumab, leading oncologists are using circulating tumor DNA (ctDNA) clearance in clinical practice to increase confidence and facilitate shared decision-making around stopping treatment, despite it not being standard of care.

The INVIGOR-11 trial data should be applied carefully. A positive ctDNA result post-surgery indicates when to *initiate* adjuvant immunotherapy. However, if a patient on neoadjuvant therapy becomes ctDNA-negative, this signals treatment efficacy and is a reason to *continue* the planned course, not a justification for stopping it early.

For colorectal cancer patients in surveillance, serial ctDNA testing offers profound reassurance. Data shows that after achieving one year of consistently negative results, the probability of a future recurrence drops to just 0.9%, providing a level of confidence previously unattainable with other methods.

The type of treatment inducing ctDNA clearance matters. Clearance from immunotherapy appears to be more permanent and strongly prognostic than clearance from chemotherapy, which can be transient. This suggests immunotherapy may achieve a more profound and lasting elimination of cancer cells versus cytotoxic agents.

While not yet validated, ctDNA is being used by clinical experts as a de-escalation tool to provide confidence when stopping long-term maintenance therapies like PARP inhibitors. This novel application focuses on reducing treatment burden rather than solely detecting disease progression.

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.

Circulating tumor DNA (ctDNA) testing is described as unequivocally the most prognostic tool available for colorectal cancer. Patients who remain serially negative have a minimal recurrence risk, while a positive result almost universally predicts a future clinical recurrence by 6-8 months.

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.