Key points
- The scale compares FDG uptake with background, the mediastinal blood pool and the liver.
- Lower and higher numbers describe relative uptake. They do not measure tumor size.
- The CT part may still show a residual mass even when PET response criteria describe complete metabolic response.
- A score must be read with scan timing, change from baseline, symptoms, treatment and specialist review.
What PET/CT measures
Before an FDG PET scan, a small amount of radioactive glucose-like tracer is given. Tissues take it up at different levels. Lymphoma can be FDG-avid, but uptake is not unique to lymphoma. Infection, inflammation, healing and normal organs can also show activity.
The Deauville scale gives the interpreting specialist common reference points inside the same scan. This is more useful than treating one SUV number as a universal threshold.
What scores 1 to 5 describe
The definitions below summarize the Deauville five-point scale used in the Lugano lymphoma response framework:
- Score 1
- No uptake above background in the area being assessed.
- Score 2
- Uptake at or below the mediastinal blood-pool reference.
- Score 3
- Uptake above the mediastinal reference but at or below liver activity.
- Score 4
- Uptake moderately above liver activity.
- Score 5
- Uptake markedly above liver activity and/or new FDG-avid lesions considered related to lymphoma.
Reports can use additional wording because specialists also compare the scan with baseline and earlier images. “Score 4” or “score 5” alone does not show whether uptake has fallen, stayed stable or increased.
How response language uses the score
Under the Lugano response classification, scores 1 to 3 at an end-of-treatment assessment usually meet the imaging definition of complete metabolic response, with or without a mass still visible on CT. Scores 4 and 5 use the change from baseline and scan timing to distinguish response categories.
Interim and end-of-treatment scans answer different questions. A score during treatment may describe response in progress. The same number after treatment enters a different clinical discussion. Do not transfer wording from someone else's report to yours without that context.
“Residual mass” describes tissue still visible on imaging. “FDG uptake” describes metabolic activity. “Deauville score” compares that activity with reference tissues. They are connected, but they are not three names for the same thing.
Why PMBCL needs careful context
PMBCL often begins as a large mediastinal mass. After treatment, tissue and FDG uptake can remain for reasons other than active lymphoma. Research after DA-EPOCH-R found that one end-of-treatment PET scan alone did not reliably separate every inflammatory finding from residual disease. Specialist teams may use image review, change over time, another scan or biopsy when results are unclear.
This does not make a higher score safe to ignore. It means the next step should come from the lymphoma team rather than a number interpreted in isolation.
Questions for your medical team
- Is this an interim scan or an end-of-treatment scan?
- What is the Deauville score, and which area determined it?
- How has uptake changed from the baseline or previous scan?
- Does the CT show a residual mass, and has its size changed?
- Could treatment-related inflammation or scan timing affect this result?
- What does the multidisciplinary team think the finding represents?
- What happens next, and what information would change that plan?
- When should I contact you before the next planned appointment?
Medical sources
Claims above link to these sources. Links checked 23 July 2026.