End-of-Treatment PET in Lymphoma — What Your Result Means

A complete metabolic response, or CMR, means the scan found no FDG uptake in previous lymphoma sites that exceeds the reference thresholds in the Deauville scoring system. It is the result the treatment team is aiming for. CMR does not mean the scan found nothing at all — it means that any tissue still visible on the CT portion of the scan is no longer metabolically active at a level that meets the threshold for residual disease. Your haematologist will confirm what this means for your follow-up plan.

The Deauville scale is a standardised five-point grading system that radiologists use to describe residual FDG uptake in lymphoma after treatment. It compares uptake in each area of concern to two reference points in your body — the mediastinal blood pool and the liver — rather than to an absolute number. Using shared reference points means results are more consistent between different centres and different scanners. Your haematologist uses the Deauville score alongside your lymphoma type and clinical picture to decide what comes next.

Not necessarily. Lymphoma often leaves scar tissue after successful treatment, and that scar can remain visible on the CT portion of the scan for months or years. What matters is whether the tissue is FDG-avid — whether it is taking up the tracer at a level that suggests active metabolism. A residual mass with no significant FDG uptake, or uptake clearly below the reference thresholds, is not treated as active disease. Your haematologist will explain what the report says about any residual tissue visible in your case.

In most protocols the scan is done several weeks after the last treatment cycle to allow inflammation to settle. Scanning too soon after chemotherapy can produce false-positive results, because treatment itself causes metabolic activity in surrounding tissue that can look like lymphoma. Your oncology team will give you the specific date based on your treatment schedule and lymphoma type. If you are unsure when your scan should happen, ask at your next appointment rather than booking independently.

PET-CT has limits on what it can detect. Small numbers of lymphoma cells below the scanner's detection threshold will not appear as a positive result. This is why a complete metabolic response is described as no detectable residual disease, not as confirmed absence of all disease. It is also why follow-up continues after a normal scan — clinical examination and blood tests during the surveillance period provide additional reassurance, and any new symptoms should be reported promptly rather than assumed to be unrelated.

Ask your haematologist to explain the Deauville score in plain terms, what the result means for your specific lymphoma type, and what the follow-up plan looks like from here. If your response is not a complete metabolic response, ask what the next step involves and what it is expected to achieve. Write the answers down, or ask whether a nurse or coordinator can follow up in writing. It is entirely reasonable to ask for a second opinion on a difficult or borderline result.