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18F-fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) is currently used to determine the therapeutic response of patients with multiple myeloma (MM). It is used to delineate myeloma bone or extramedullary (EMD) lesions, evaluate tumor metabolic activity, and monitor treatment response. Following the International Myeloma Working Group (IMWG) criteria, it is essential to measure the measurable residual disease, but also the complete metabolic response (CMR), inside and outside the bone marrow (BM).1 In the absence of standard imaging criteria for PET CMR, a combined analysis of two prospective imaging substudies from large phase III trials (IFM/DFCI 20092 and EMN02/HO953) was conducted. Both trials enrolled transplant-eligible patients with newly diagnosed MM (NDMM) and evaluated PET/CT response after therapy applying the Deauville scale (DS) without predefined cutoffs.4
The findings of this joint analysis and the suggested redefined response criteria (included at the end of this article) were published recently in the Journal of Clinical Oncology by Elena Zamagni and colleagues and are summarized here.4
The imaging subanalysis involved two trials, IFM/DFCI 2009 and EMN02/HO95, enrolling a total of 228 transplant-eligible patients with NDMM.
PET/CT scans analyzed jointly were only at baseline and PM in an effort to standardize PET/CT evaluation and define criteria for PET CMR after therapy by determining the prognostic impact of such assessment on PFS. The five-point DS was used to describe BM score (BMS) and focal lesion (FL; FL score [FS]) uptake.
Parameters of physiological interest related to reference organs, liver, and mediastinal blood pool (MBP) were measured using a spherical volume of interest with a radius > 3 cm in the central portion of the liver and a volume of interest within the aorta lumen.
Table 1. PET/CT assessment before maintenance therapy (PM)4
PET/CT results |
Overall |
IFM/DFCI 2009 |
EMN02/H095 |
---|---|---|---|
BM, bone marrow; CT, computed tomography; DS, Deauville scale; FL, focal lesion; IQR, interquartile range; PET, positron emission tomography; PM, premaintenance; SUVmax, maximum standardized uptake value. |
|||
Number of patients |
199 |
119 |
80 |
Presence of FL uptake, DS score* |
62 (31.2) |
24 (20.2) |
38 (47.5) |
2 |
5 (8.1) |
0 (0.0) |
5 (13.2) |
3 |
15 (24.2) |
1 (4.2) |
14 (36.9) |
4 |
36 (58.0) |
20 (83.3) |
16 (42.1) |
5 |
6 (9.7) |
3 (12.5) |
3 (7.9) |
Presence of BM uptake, DS score* |
195 (98.5) |
118 (100.0) |
77 (96.3) |
2 |
103 (52.8) |
63 (53.5) |
40 (51.9) |
3 |
75 (38.5) |
43 (36.4) |
32 (41.6) |
4 |
16 (8.2) |
11 (9.3) |
5 (6.5) |
5 |
1 (0.5) |
1 (0.8) |
0 (0.0) |
Median BM SUVmax (IQR) |
2.30 (1.80–3.08) |
2.60 (2.10–3.40) |
1.85 (1.54–2.51) |
Median FL SUVmax (IQR) |
3.67 (2.71–5.02) |
5.37 (4.20–6.93) |
3.07 (2.30–3.85) |
FDG-PET/CT is a reliable technique to predict outcomes in patients with NDMM, especially post-ASCT. Reduced FL and BM FDG uptake compared with the liver represent the standardized definition of PET CMR before maintenance under the newly proposed PET response criteria (Table 2), indicating sustained disease control. In both BM and FLs, a DS score of < 4 (with the liver uptake as reference) is the strongest predictor of improved PFS and OS.
However, clinical studies with independent prospective series of patients extensively applying measurable residual disease techniques at the BM level and imaging are still needed to validate and redefine the role of PET CMR and PET response criteria in treating patients with MM inside and outside clinical trials.
Table 2. Proposed refinement of PET response criteria before maintenance4
PET response before maintenance |
Response criteria |
---|---|
BM, bone marrow; DS, Deauville scale; FL, focal lesion; PET, positron emission tomography. |
|
Complete metabolic response |
Uptake ≤ liver activity in BM sites and FLs previously involved, including extramedullary and paramedullary disease (DS score 1–3) |
Partial metabolic response |
Decrease in number and/or activity of BM/FLs present at baseline, but persistence of lesion(s) with uptake > liver activity (DS score 4 or 5) |
Stable metabolic disease |
No significant change in BM/FLs compared with baseline |
Progressive metabolic disease |
New FLs compared with baseline consistent with myeloma |
Despite not being perfect, FDG-PET/CT is currently the recommended imaging technique in MM to evaluate metabolic response to therapy. Many prospective and retrospective studies are confirming over time its relevant prognostic value for predicting the risk of relapse and death after therapy, even in the context of newer novel agent combinations. This first attempt to standardize the interpretation of the results after therapy and, in particular, to provide a precise definition of complete metabolic response will allow to compare the results of different trials and more easily apply FDG-PET/CT in routine clinical practice. The new criteria are currently under validation in independent prospective trials; initial results seem to highlight the applicability and reproducibility. Other techniques such as diffusion-weighted magnetic resonance imaging (DW-MRI) enrich the opportunities, all directed to the best patient treatment.
References
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