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.

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.

Circulating tumor DNA (ctDNA) identifies post-surgery patients at high risk of relapse. By targeting adjuvant immunotherapy to only this ctDNA-positive group, previously negative clinical trials demonstrate a significant survival benefit. This approach spares low-risk, ctDNA-negative patients from unnecessary treatment and toxicity.

Circulating tumor DNA (ctDNA) is a powerful biomarker for identifying high-risk bladder cancer patients. However, its imperfection presents a new clinical dilemma: with a ~12% relapse rate even in ctDNA-negative patients, clinicians must decide whether to withhold adjuvant therapy and accept that risk, or overtreat the 88% who are likely cured.

In adjuvant bladder cancer trials, ctDNA status is both prognostic and predictive. Patients with positive ctDNA after surgery are at high risk of relapse but benefit from immune checkpoint inhibitors. Conversely, ctDNA-negative patients have a lower risk and derive no benefit, making ctDNA a critical tool to avoid unnecessary, toxic therapy.

An overall survival (OS) benefit in an adjuvant trial may not be meaningful for patients in systems (e.g., the U.S.) with guaranteed access to the same effective immunotherapy upon recurrence. The crucial, unanswered question is whether treating micrometastatic disease is inherently superior to treating macroscopic disease later, a distinction current trial data doesn't clarify.

For ctDNA-positive patients with high relapse risk, a clinical conflict arises. 'Purists' advocate for treatments with prospective trial data (single-agent immunotherapy), while 'pragmatists' argue for using the most effective therapy available (like EV pembro), treating ctDNA positivity as early metastatic disease, even without specific trial evidence in that setting.

A critical warning for clinicians: data showing that ctDNA-negative patients can skip *adjuvant* therapy (InVigor011) should not be extrapolated to the *neoadjuvant* setting. Stopping the post-operative portion of a perioperative EV-Pembro regimen based on a negative ctDNA result is unsupported by data and risks under-treating patients.

A positive ctDNA result post-surgery in an immunotherapy-naive patient warrants starting treatment. Conversely, if a patient received neoadjuvant immunotherapy and remains ctDNA positive after surgery, it signals resistance, making continuation of the same therapy illogical and creating a clinical paradox.