Prognostic Impact of Minimal Residual Disease By ASO-RQ-PCR in Multiple Myeloma: A Pooled Analysis of 2 Phase III Studies in Patients Treated with Lenalidomide after Front-Line Therapy

Background: The prognostic utility of minimal residual disease (MRD) analysis in multiple myeloma (MM) patients has been well described in the last few years. The role of prolonged maintenance therapy even in persistent MRD negative patients is still unclear. The aim of this study is to evaluate the role of MRD by allelic-specific oligonucleotide real-time quantitative polymerase chain reaction (ASO-RQ-PCR) as predictor of progression-free survival (PFS) in newly diagnosed MM (NDMM) patients receiving Lenalidomide maintenance after frontline treatment.

Patients and Methods: NDMM patients enrolled in the RV-MM-EMN-441 (NCT01091831) and the RV-MM-COOP-0556 (EMN02/HO95 MM) phase III trials achieving ≥ very good partial response (VGPR) after consolidation/intensification were included in the pooled MRD molecular analysis. After induction therapy, patients in the RV-MM-EMN-441 study were randomized to Cyclophosphamide-Lenalidomide-Dexamethasone (CRD) or Autologous Stem Cell Transplantation (ASCT); patients in the RV-MM-COOP-0556 were randomized to Bortezomib-Melphalan-Prednisone (VMP) vs ASCT (Gay F et al Lancet Oncol 2016, Cavo M et al J Clin Oncol 34, 2016 abstr 8000). All patients received Lenalidomide maintenance until progression or intolerance. MRD analysis was performed on bone marrow (BM) aspirates after intensification/consolidation, after 6 courses of maintenance and then every 6 months until clinical relapse. Patient-specific IgH rearrangements were amplified and directly sequenced from genomic DNA at diagnosis. IgH-based MRD detection by ASO-RQ-PCR was performed using an AbiPrism7900HT.MRD analysis was interpreted following the Euro-MRD guidelines(van der Velden VH et al. Leukemia 2007). Molecular-CR (m-CR) was defined as two consecutive negative MRD results by ASO-RQ-PCR with minimal sensitivity of 10⁻⁵. PFS was analyzed using the Kaplan-Meier method, curves were compared with the log-rank test. Multivariate Cox model was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs).

Results: a total of 105 patients entered the molecular MRD pooled study: a specific IgH molecular marker was identified in 73 patients (70%), 32 (30%) did not obtain a successful sequencing. Median age was 57 years (37-65); 30 (41%) patients had International Staging System (ISS) stage I, 33 (45%) stage II and 10 (14%) stage III. FISH risk profile was standard in 43 (59%) patients, high in 24 (33%) and not available in 6 (8%). Thirty-eight (52%) patients did not receive ASCT consolidation and 35 (48%) underwent ASCT. After consolidation/intensification 33/73 (45%) patients achieved m-CR: 19/35 (54%) ASCT patients and 14/38 (37%) no ASCT patients. The impact of m-CR on outcome after consolidation was explored: after a median follow-up of 44 months, median PFS was 48.8 months versus not reached in no m-CR vs m-CR patients, respectively (p=0.01). Lenalidomide maintenance further improved depth of MRD response: 11/40 (27%) MRD positive patients after consolidation obtained a m-CR during maintenance and a median of 2 natural logarithms of tumor burden reduction was recorded.

In multivariable Cox analysis the risk of progression/death was higher for ISS stage II/III versus I (HR, 2.91, CI: 1.01-8.41, p=0.048), high-risk FISH versus standard-risk (HR, 2.23 CI: 0.81-6.10, p=0.12), age > 60 years versus ≤60 years (HR: 3.55, CI: 1.26-10.04, p=0.017) and patients who did not achieve m-CR during treatment versus patients who did (HR, 7.65 CI: 2.77-21.11, p<0.001).

We identified a very high risk group defined by high risk FISH at diagnosis and persistent MRD positivity, with a median PFS of 29.4 months (figure1).

Conclusions: MRD status by ASO-RQ-PCR is a predictor of outcome significantly superior to standard risk factors in NDMM patients and the achievement of m-CR seems to overcome the high risk FISH status in PFS analysis. Molecular CR rate and reduction of tumor burden obtained after consolidation can be enhanced with Lenalidomide maintenance. Based on these preliminary results, the assessment and monitoring of MRD should be suggested as a better prognostic indicator than CR, and the potential role of a MRD-guided therapy should be investigated in future prospective trials.

Figure 1

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PFS of patients stratified by MRD status (molecular-CR vs no molecular-CR) and FISH (high risk vs standard risk)

Figure 1

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PFS of patients stratified by MRD status (molecular-CR vs no molecular-CR) and FISH (high risk vs standard risk)

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