What Is a Deauville 3 — and Why Is It Ambiguous?

It is genuinely neither without more context. In many end-of-treatment scans, a 3 is counted as a complete metabolic response under the Lugano criteria — which is a positive outcome. In some interim assessments, the same score may be treated as insufficient response, depending on the protocol. The answer depends on when your scan was done, your cancer type, and the framework your team is working from. Ask your oncologist which definition applies to your situation.

Not necessarily, and this is the central source of anxiety around this score. A 3 means there is uptake above the mediastinum but no higher than the liver. That can represent residual active cancer, but it can also represent inflammation, post-treatment tissue change, or normal metabolic variation. Whether it is read as active disease or as a response depends on your protocol and on the other clinical information your team is weighing alongside the number.

Because under the Lugano criteria — the international framework endorsed by ESMO and ASCO — a Deauville 3 at end of treatment is classified as complete metabolic response in many lymphoma types. Your oncologist is applying that framework correctly. It can feel counterintuitive when there is still some uptake showing, but the scale was designed with that threshold deliberately, because uptake at or below liver level does not reliably distinguish active disease from normal variation.

Sometimes, but not always. A biopsy may be recommended if your oncologist is uncertain whether a 3 represents residual active disease or post-treatment change, particularly if a mass is still visible on imaging or other clinical signs raise concern. In many cases a 3 that fits the expected pattern of response is managed with a repeat scan rather than a biopsy. That decision is specific to your situation, and your team is the right person to explain the reasoning behind your plan.

Yes, and it is entirely reasonable, especially when a significant decision rests on the interpretation. A second nuclear medicine physician or radiologist with lymphoma expertise may review the same images. The score itself may or may not change, but a second opinion on how it should be interpreted in your clinical context can give you confidence in the plan. Your current team can usually arrange this, or you can ask for your imaging files to take to another centre.

Yes. Hodgkin lymphoma and diffuse large B-cell lymphoma — along with other subtypes — each have their own response criteria and their own evidence base for how a 3 should be handled at interim and at end of treatment. Studies that established the evidence around interim PET-CT used different cutoff definitions for different disease types. This is one reason why a single number does not carry a universal meaning, and why your oncologist's interpretation is specific to your diagnosis.