One of the most substantial changes between the 1999 IWG-NHL criteria and the revised 2007 IWG-NHL criteria is regarding the incorporation of FDG-PET into the assessment.
The primary use of FDG-PET is to differentiate PR (SD) from true CR and to eliminate the CRu category.
When Progression Free Survival (PFS) is the primary endpoint:
- The lack of FDG-PET has little or no effect.
When Complete Remission rate is the primary endpoint:
- Differentiation of CR from PR is crucial.
Clear rules must be defined for the case where PET is not routinely available; in those instances Perceptive Informatics recommends that CT/MRI measurements are used to define response.
Using PET - If FDG-avid disease
Lymphoma subtypes which are FDG-avid have the greatest potential benefit of incorporating PET into response assessment.
At baseline, each lesion should be assessed for FDG-avidity and only FDG-avid lesions should be selected as target lesions.
- If a lesion was present and clearly abnormal by CT/MRI but PET-negative at baseline, it should be followed as a non-target using the CT/MRI images.
- Conversely, if that previously PET-negative lesion becomes PET-positive and cannot be attributed to a non-lymphomatous cause, that change in PET status (negative to positive) should be considered indicative of progression.
- If a lesion is PET-positive at baseline but becomes PET-negative at follow-up, then CR is possible regardless of size on CT/MRI. If a lesion was PET-positive at baseline and remains PET-positive at follow-up, the assessment for that lesion should be based on CT/MRI assessment and CR would not be possible.
- If no PET is available at baseline, all lesions should be assumed to be FDG-avid. At follow-up, if PET became available, FDG-avidity in a previously present lesion would not be considered progression. At follow-up a lesion must be PET-negative to be considered CR.
- If no PET is available at follow-up, the assessment should be based on the CT/MRI.
Using FDG-PET - If Variable FDG-avid disease type
Incorporating PET for variable PET FDG-avid disease may also provide a benefit to deriving response assessment.
If PET is not available at baseline, all lesions should be assumed PET-negative.
- At follow-up, if a lesion is PET-negative, the assessment should be based on CT/MRI measurements.
- If a lesion is PET-positive at follow-up, the patient cannot be considered a CR.
If PET is available at baseline, each lesion should be assessed for FDG-avidity.
- If a lesion is PET-positive at follow-up, the patient cannot be considered a CR and the assessment would be based on CT/MRI assessments.
- If a lesion is PET-negative at follow-up and was FDG-avid at baseline, CR is possible regardless of lesion size on CT/MRI assessment.
- If a lesion was PET-negative at baseline, CR is only possible if the lesion is normal by CT/MRI assessment.
- If a lesion was PET-negative at baseline, but FDG-avid at follow-up, then progression has occurred.