Minimal Residual Disease (MRD) Testing in Newly Diagnosed Multiple myeloma (MM) Patients: A Prospective Head-to-Head Assessment of Cell-Based, Molecular, and Molecular-Imaging Modalities

*Equally Contributed

Introduction: Recent studies show better progression-free (PFS) and overall survival (OS) for newly diagnosed multiple myeloma (NDMM) pts achieving MRD negativity by multicolor flow cytometry (MFC) or next-generation sequencing (NGS). Here, we report on the comprehensive assessment of MRD in a uniformly treated cohort of 45 MM patients (Korde et al. ASH 2013).

Methods: 45 NDMM pts were treated with 8 cycles of combination therapy (carfilzomib, lenalidomide and dexamethasone) followed by 2 years of maintenance lenalidomide. Median potential follow-up was 17.3 mos. All patients were evaluated by NGS by LymphoSIGHT™ method. Briefly, using universal primer sets, we amplified immunoglobulin heavy and kappa chain (IGH and IGK) variable, diversity, and joining (VDJ) gene segments from genomic DNA obtained from CD138+ BM cell lysate or cell free bone marrow (BM) aspirate at baseline. A MM clonotype was defined as an immunoglobulin rearrangement identified by NGS at a frequency >=5%. MRD assessment by NGS, MFC and PET was repeated when patients achieved a complete response (CR) or completed 8 cycles of therapy. In a subset of patients, we performed NGS in peripheral blood (plasma) at baseline and after 2 cycles of treatment.

Results:

40/45 (89%) of pts achieved VGPR or better after combination therapy. At least one clonal rearrangement was identified in 31/34 (91%) of BM CD138+ cell samples and in 34/45 (76%) of cell free BM aspirates; overall clonal rearrangement was detected in 37/45 (82%) bone marrow aspirates at baseline. Repeat MRD assessment at CR or the completion of 8 cycles in 32 pts show residual disease in cell free BM aspirates by NGS in 18 (56% of pts tested and 40% of the total study population). Estimated 12-mo and 18-mo PFS for MRD neg vs. pos by NGS was 100% vs 94% and 100% vs 84%, respectively (p=0.025). MFC testing for MRD was feasible in 43/44 pts (98%). PFS probabilities at 12-mo and 18-mo for flow neg vs pos was 100% vs 79% and 100% vs 63%, respectively (p=0.0022). Among pts assessed by both MRD methods (n=31), 23 samples were concordant (9 pos and 14 neg); among 8 discordant cases, all were positive by sequencing and negative by flow (p=0.0078). Abnormal PET scans were noted in 38/45 (84%) of pts at baseline. 24/43 (56%) pts at CR or after 8 cycles of CRd had a neg/dec PET response and 19/43 (44%) pts had a pos/partial PET response. At 12-mo and 18-mo, PFS by a neg/dec PET response vs pos/partial PET response was 100% vs 89% and 92% vs 89%, respectively (p=0.54). Furthermore, in 14 pts, we performed NGS in peripheral blood samples collected at baseline. At least one MM clonotype identified in baseline BM was detectable in corresponding plasma sample in 13/14 pts. Number of myeloma-specific molecules per million diploid genomes in the plasma was 3-log fold lower than in the BM (median 252 vs 730,950 MM specific clonal molecules per million diploid genomes). After 2 cycles of CRd treatment, 12/13 pts were still pos by serum electrophoresis and/or immunofixation while only 1 had detectable myeloma clonotypes in the plasma.

Conclusions: This prospective evaluation of MRD testing in MM has several key findings: 1. Detection of myeloma-specific clonotypes by NGS of the Immunoglobulin VDJ segments in the BM is feasible in majority of pts with NDMM. 2. MRD detection by NGS compares favorably to MFC since all pts with residual disease by MFC are also MRD positive by sequencing; an additional 8 pts who were MRD negative by flow MFC were MRD positive by sequencing. 3. MRD negativity by MFC and NGS are both associated with significantly better PFS. 4. Detection of myeloma-specific clonotypes by NGS of the immunoglobulin VDJ segments (i.e. cell free DNA) in the peripheral blood plasma is feasible in NDMM pts at diagnosis; however, since tumor load in the plasma is >2000-fold lower than in the BM; using standard volumes of peripheral blood (plasma), the levels of myeloma-specific clonotypes were too low to be quantified already after 2 cycles of combination therapy. This was true despite presence of positive serum electrophoresis and/or immunofixation. Additional studies to understand the dynamics of the myeloma clonotype level in peripheral blood plasma are necessary to determine optimal MRD testing regimen.