Prospective Evaluation of 18F-FDG PET/CT As Predictor of Prognosis in Newly Diagnosed Transplant Eligible Multiple Myeloma (MM) Patients: Results from the Imaging Sus-Study of the EMN02/HO95 MM Randomized Phase III Trial

F-18-fluorodeoxyglucose positron emission tomography integrated with computed tomography (FDG-PET/CT) enables to detect with relatively high sensitivity and specificity myeloma bone disease and extramedullary sites of metabolically active clonal plasma cells. FDG-PET/CT has also been used to assess and monitor the metabolic response to therapy and to predict the prognosis. One of the major limitation of PET/CT is the lack of standardized image criteria and of inter-observer reproducibility in interpreting the results.

Aim of the present sub-study was to prospectively evaluate FDG-PET/CT at diagnosis, after 4 cycles of induction therapy and prior to maintenance therapy in a sub-group of patients enrolled into EMN02/HO95 MM international phase III trial. In particular, the two primary end-points were firstly to assess the prognostic significance of PET/CT at diagnosis and after therapy and secondly to standardize PET/CT evaluation by centralized imaging and revision and definition of criteria for interpretation.

Seven hundred and 18 patients with newly diagnosed transplant-eligible symptomatic MM have been prospectively randomized in Italy from February 2011 through April 2014 to receive 4 cycles of bortezomib-melphalan-prednisone (VMP) vs high-dose melphalan and single or double autologous stem cell transplantation (ASCT) as intensification following induction with bortezomib-cyclophosphamide-dexamethasone (VCD). Consolidation therapy with bortezomib-lenalidomide-dexamethasone vs no consolidation was planned after VMP or ASCT(s), followed by lenalidomide maintenance until progression or toxicity. One hundred and three patients were included in the PET/CT imaging sub-study, and followed for a median of 24 months. By study design, PET/CT was performed and analysed in each of the 8 participating centres at baseline, after induction therapy and prior to the start of maintenance (EOT). Each PET scan was a posteriori re-interpreted in a blinded independent central review process, managed by WIDEN®, by a panel of 5 expert nuclear medicine physicians. They described the following characteristics: bone marrow metabolic state (BM), number (Fx) and score (Fs) of focal PET positive lesions, osteolysis (Lx), presence and site of extramedullary disease (EM), and fractures(Fr), according to the IMPeTUs criteria (Nanni et al, EJNM 2015). Moreover, a global score (GS), from 1 to 5, was given to each patient, considering the highest score among BM, Fx, Fs and EM. Concordance among reviewers on different metrics was calculated using Krippendorf's alpha (AK) coefficient

Baseline characteristics of the patients were the following: median age 58 years, ISS and R-ISS stage III 15% and 10%, high-risk cytogenetics (t(4;14) ± del(17p) ±del (1p)±1q gain detected by FISH) 42%.

At baseline, 78% of the patients had FLs, with a median SUVmax of 6.0. The percentages of PET positive patients for the different characteristics are summarized in table 1. The agreement among reviewer was good for BM (AK=0.49), Fx (AK=0.65), Fs (AK=0.62), Lx (AK=0.62) and EM (AK=0.40). Of all parameters, only Fx ≥ 4 was associated with worse PFS and OS (P = 0.06)

Following 4 cycles of VCD, PET/CT remained positive in 59% of the patients, with a median SUVmax of 3.7. Of all parameters, only Fs ≥ 4 was predictive of worse OS (P= 0.05).

Prior to maintenance therapy, PET/CT remained positive in 34% of the patients, with a median SUVmax of 3.4. Normal PET/CT findings before maintenance (66%) were associated with a significant improvement in PFS, in particular the following: presence of FLs (P=0.03), Fx ≥ 4 (P=0.001), Fs ≥2 (P=0.03), 3 (P=0.03) and 4 (P=0.006) and SUVmax ≥ 3.4 (p=0.002). GS was also predictive for PFS if ≥ 3 (P=0.033), 4 (P=0.0001) and 5 (P=0.004). The same parameters were also predictive for OS. The prognostic relevance of pre-maintenance PET/CT was retained across the randomization arm (VMP or ASCT), in terms of PFS and OS.

In conclusion, PET/CT was confirmed to be a reliable predictor of outcome in newly diagnosed transplant eligible MM patients, whatever the treatment. Normalization of PET/CT before maintenance was associated with a significant improvement for PFS and OS. FDG-PET/CT is by now the preferred imaging technique for evaluating and monitoring response to therapy.

Acknowledgments: this study was partially supported by a grant to Elena Zamagni from Fondazione del Monte di Bologna e Ravenna

Table 1

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Table 1

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