Response assessment
PERCIST Criteria: — Reading Your Metabolic Response
PERCIST is the formal scoring system used to measure how a tumour's metabolic activity has changed on a PET scan after treatment. The four categories in your report — CMR, PMR, SMD, PMD — each have a specific meaning, and understanding them helps you follow the conversation with your oncologist.
Medically reviewed by Dr. C. Raghavendra Reddy, Medical Oncologist, MBBS (Gold Medal) · DNB · DM (Medical Oncology, Gold Medal) · Last reviewed September 2026
- Metabolic, not physical — PERCIST measures activity inside the tumour on PET, not whether it has shrunk on CT.
- Four clear categories — CMR, PMR, SMD, and PMD describe the range from full metabolic response to progression.
- Response can show early — Metabolic changes on PET can appear before the tumour physically shrinks, so PERCIST and RECIST can tell different stories at the same point in treatment.
- Your oncologist reads the result — The category in your report is one input into a clinical decision — it does not decide what happens next on its own.
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PERCIST is a standardised set of criteria used to measure how much a tumour's metabolic activity has changed on a PET scan after treatment. Your report uses one of four categories — CMR, PMR, SMD, or PMD — to describe the change. Your oncologist interprets what the result means for your next steps.
What do the words in your PERCIST report mean?
- PERCIST
- PET Response Criteria in Solid Tumours. The formal framework for grading how much metabolic activity has changed in a tumour on a PET scan, usually compared to a baseline scan done before or at the start of treatment.
- SULpeak
- The measurement PERCIST uses to quantify metabolic activity. It adjusts for the patient's lean body mass, making the number more comparable between one scan and the next than a basic SUV.
- Target lesion
- The one area of highest metabolic activity chosen from the baseline PET scan. All follow-up scans compare the same lesion against that starting point.
- CMR — Complete Metabolic Response
- No measurable metabolic activity remains in the target lesion above background levels. Commonly described as a clear scan.
- PMR — Partial Metabolic Response
- The target lesion shows a meaningful reduction in metabolic activity compared to the baseline. The cancer is responding to treatment as measured on PET.
- SMD — Stable Metabolic Disease
- The target lesion has changed, but not enough to meet the threshold for response or progression. Also reported as stable or no significant change.
- PMD — Progressive Metabolic Disease
- The target lesion shows a meaningful increase in metabolic activity, or a new metabolically active area has appeared. The cancer is not responding as measured on PET.
How is PERCIST different from RECIST?
RECIST measures whether a tumour has physically grown or shrunk on a CT or MRI scan. PERCIST measures whether the tumour's metabolic activity — how actively it is consuming glucose — has changed on a PET scan.
These are two different questions, and they can produce different answers at the same moment in treatment. A tumour can still look the same size on CT while its metabolic activity has already dropped significantly on PET.
Your team may use one or both systems depending on your cancer type, the treatment you are on, and what the scan is being ordered to answer.
How do PERCIST and RECIST compare?
| Feature | PERCIST | RECIST 1.1 |
|---|---|---|
| What it measures | Metabolic activity on PET | Physical tumour size on CT or MRI |
| Scan required | FDG-PET | CT or MRI |
| Response categories | CMR, PMR, SMD, PMD | CR, PR, SD, PD |
| Number of target lesions | One — most metabolically active | Up to five |
| Early response detection | Often, before size changes | Only once the tumour physically shrinks |
| Commonly applied in | Lymphoma, lung, oesophageal, head and neck | Most solid tumours in clinical trials |
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Who uses PERCIST, and when does your team order it?
PERCIST is used for cancers where FDG-PET reliably shows metabolic activity — lymphoma is the most common example, followed by certain lung, oesophageal, and head and neck cancers.
Your team orders a response-assessment PET to answer a specific clinical question: is the treatment working well enough to continue, or does the plan need to change? The timing of the scan is chosen to give it the best chance of showing a meaningful difference.
Not all cancers are assessed with PERCIST. For many solid tumours, RECIST on CT remains the standard. Your oncologist will tell you which framework applies to your situation.
What should you do when you receive a PERCIST report?
- Note which category your result falls into: CMR, PMR, SMD, or PMD.
- Write down your questions before seeing your oncologist — the report is easier to discuss when you have it with you.
- Ask how this result compares to your previous scan.
- Ask what this result means for your treatment plan — does it continue, change, or pause?
- Ask whether another scan has been scheduled, and what it is looking for.
- Do not compare your result to another person's — the same category can mean different things depending on the cancer, the treatment, and the baseline.
What else should I understand about my PERCIST result?
Does CMR mean I am cured?
CMR means no measurable metabolic activity was detected in the target lesion at the time of the scan. It does not confirm that every cancer cell is gone, and it does not mean treatment is necessarily over. What CMR means for your next steps — whether you continue the same treatment, move to a different phase, or enter surveillance — depends on your cancer type and the protocol your team is following. Your oncologist will explain what CMR means in your specific situation.
My report says PMD but my tumour looks the same size. How can that happen?
PERCIST and RECIST measure different things, and they do not always agree. PERCIST detects changes in metabolic activity — how actively the cancer cells are consuming glucose — while size on CT reflects physical bulk. A tumour can still look unchanged in size while becoming more metabolically active internally, particularly early in progression. When the two give different signals, your oncologist weighs both results alongside your symptoms and clinical picture before deciding on next steps.
My previous scan used RECIST. Why has my team switched to PERCIST?
Different scans answer different questions at different stages of treatment. Your team may order a PET with PERCIST assessment when they want to know about metabolic activity rather than size — for example, after chemotherapy in lymphoma, or to look for active disease before planned surgery. A change in assessment method does not mean your situation has changed; it means the clinical question has changed. Ask your team what specific question the new scan was ordered to answer.
What happens after a PMR result?
PMR means the treatment is producing a measurable metabolic response, and in many cases treatment continues with another assessment planned. What happens next depends on your cancer type, the degree of reduction, and what the protocol specifies. In some situations a PMR at an interim scan is enough to continue; in others the team may be looking for CMR before moving to the next phase. Ask your oncologist what the target for your treatment is and whether your result meets it.
Is PERCIST used for all types of cancer?
No. PERCIST requires the tumour to take up FDG reliably on PET, which not all cancers do. It is most established in lymphoma and in several solid tumours including certain lung, oesophageal, and head and neck cancers. For cancers that are not reliably FDG-avid, RECIST on CT or MRI remains the standard approach to response assessment. Your oncologist will tell you whether PERCIST is the appropriate framework for your cancer type.
Can I compare my result to someone else's in a support group?
Not meaningfully. The same PERCIST category can carry very different implications depending on the cancer type, the treatment being assessed, the timing of the scan, and the baseline it is being compared against. A CMR in one lymphoma subtype at a specific interim point means something quite different from a CMR in a different cancer at a different stage. Use your result as the basis for a conversation with your own oncologist rather than as a benchmark against another person's experience.
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Explore 94 more Understanding Your PET-CT Report topics
Response Assessment Scores & Criteria
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- Deauville Score 1 to 5: The Lymphoma Scale Explained
- End-of-Treatment PET Scan: What It Decides
- How Doctors Judge Whether Treatment Is Working on PET-CT
- Interim PET Scan During Chemotherapy: Why It Is Done
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- PERCIST Criteria: How Metabolic Response Is Measured
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Common questions
Frequently asked questions
What does PERCIST stand for?
PERCIST stands for PET Response Criteria in Solid Tumours. It is a formal set of criteria developed to standardise how metabolic response is reported on FDG-PET scans, so that results can be compared across scans, centres, and clinical trials. The framework was described by Wahl et al. and has since been adopted in clinical practice for cancers where PET is the standard imaging tool for response assessment.
Why does my report mention SULpeak instead of SUV?
SUV (standardised uptake value) is the basic measure of how much glucose a tissue area takes up on PET. SULpeak is a refinement used in PERCIST that adjusts for the patient's lean body mass and focuses on the most metabolically active point within the target lesion. This makes the number more consistent between scans taken at different times and more comparable between patients of different body compositions. If your report gives an SULpeak figure, it is being used for a formal PERCIST comparison rather than a rough uptake estimate.
How is the target lesion chosen for PERCIST?
On the baseline PET scan — the one taken before or at the start of treatment — the radiologist identifies the single area of highest metabolic activity. That lesion becomes the reference point for all future PERCIST assessments. Using one lesion, rather than measuring multiple sites, keeps the comparison consistent. If that lesion is no longer visible on a later scan, the criteria have specific rules for how response or progression is defined from that point.
My oncologist mentioned both PERCIST and RECIST. Do I need both?
For some cancers and some clinical questions, both are used together. PET with PERCIST gives information about metabolic activity; CT with RECIST gives information about physical size. They complement each other rather than replace each other. In lymphoma, PET is often the primary tool and size is secondary. In many other solid tumours the reverse is true. If your team is using both, ask what specific question each scan is being ordered to answer — the answer is usually straightforward.
How is PERCIST different from the Deauville score on lymphoma reports?
Both are used to assess PET scans in lymphoma, but they work differently. Deauville is a five-point visual scale that compares the target lesion's uptake to fixed reference points — the mediastinum and liver — by visual judgement. PERCIST uses a quantitative measurement, SULpeak, and defines response by how much that number has changed from the baseline scan. Some lymphoma protocols specify Deauville; others use PERCIST or both. Your report will state which framework was applied.
Does PERCIST apply to PET scans done with tracers other than FDG?
No. PERCIST was developed specifically for FDG-PET, where the tracer measures glucose uptake. Other PET tracers — such as PSMA for prostate cancer or DOTATATE for neuroendocrine tumours — measure different biological targets, and PERCIST does not formally apply to them. Those scans have their own separate response assessment frameworks. If your scan used a non-FDG tracer, ask your oncologist which criteria were used to interpret the result.