Persistent bone marrow minimal residual disease as a “high‐risk” disease feature in multiple myeloma
Authors: Meera Mohan, Aniko Szabo, Naveen Yarlagadda, Sravani Gundarlapalli, Sharmilan Thanendrarajan, Samantha Kendrick, Carolina Schinke, Daisy Alapat, Jeffrey Sawyer, Erming Tian, Guido Tricot, Frits van Rhee, Maurizio Zangari
Journal: American Journal of Hematology (2021)

While sustained minimal residual disease (MRD) negativity is an ideal therapeutic goal,1, 2 there is a subset of patients in whom MRD negativity is never achieved even with most intensive treatment approaches. In the current study, we describe the clinical characteristics and outcome of newly diagnosed multiple myeloma (NDMM) patients with continuous persistent MRD disease. NDMM patients treated in our institution between 2013 and 2019, with more than one serial BM MRD assessments regardless of disease response were included in this analysis. The frequency of MRD assessments ranged from every 3–6 months during the first 2 years of treatment to 6–12 months thereafter determined mainly by treatment phase (on or off maintenance therapy) and disease response.2, 3 All patients were treated with induction chemotherapy that included a combination of immunomodulatory agents (IMiD) and proteasome inhibitor (PI) added to a backbone of multiagent chemotherapy followed by high dose chemotherapy and autologous stem cell transplantation (ASCT) and maintenance therapy consisting of a combination of an IMiD,PI and dexamethasone.4 BM aspirate MRD assessment was performed using eight-color next generation flow cytometric (NGF) analysis with a minimal sensitivity of 10−5 cells.5, 6 Persistent MRD was defined as never attaining MRD negativity throughout the disease course. Patients who had a transient MRD negativity that lasted for ≤3 months were considered to have persistent MRD disease for this analysis. Sustained MRD negativity was defined as combined BM and imaging MRD negativity confirmed on two assessment ≥12 months apart. Patients with MRD conversion from negative to positive were excluded from the current analysis. Risk status was also assessed according to the 70 gene model (GEP70) as previously described.7 Of the 207 patients identified, 129 achieved sustained MRD negativity and 78 had persistent BM MRD positivity at all points of disease assessment. Overall, an average of 15 (range, 3–17) serial BM MRD assessments per patient were performed between 2013 and 2019. The median percentage of atypical myeloma plasma cells as determined by flow cytometry in the group with persistent MRD positivity was 0.04% (range 0.001–0.91). The median follow-up of the entire cohort from the first transplant was 2.70 (0.01–6.31) years. Baseline characteristics are shown in Table S1. In the group with persistent MRD positivity, the median age was 64 (range 56–69) years with 62% (n = 48) of patients >60 years of age; 44% (n = 34) of the patients were female and 12% (n = 9) African American. All patients received at least one autologous stem cell transplant (ASCT) and 73 of the 78 (94%) of patients received a second ASCT either planned (n = 33) or as salvage therapy (n = 40). Overall, there were no significant differences in the baseline demographics between the two groups. The distribution of GEP 70 subtypes was significantly different between the two groups. Patients with persistent MRD positivity expressed more frequently a HR GEP70 pattern (22% vs. 7.8%, p = 0.007). The distribution of CD2 subtype was 16% and 22% in the sustained MRD negative and persistent MRD positivity group, respectively. High-risk FISH markers such as (del)17p, t (14;16) and t (4;14) were observed 12% versus 17% (p = 0.5), 11% versus 12% (p = 0.9) and 6.2% versus 2% (p = 0.4), respectively and not statistically different between the two groups. On multivariate analysis, the effect of age >70 years (OR 1.18, 95% CI 0.98–1.44, p = 0.095), ISS stage III (OR 1.34, 95% CI 0.57–3.18, p = 0.5) or GEP70 HR signature (OR 2.88 95% CI 0.91–9.46, p = 0.075) were not statistically significant between the two groups, partly due to the relatively low numbers in the subgroups (Table S2). Patients with persistent residual MRD had an overall disease response (ORR) of 84% (n = 43/51); 49% (25/51) achieved ≥VGPR at 1-year post-ASCT2 (Figure S2). A second ASCT was performed in 94% (n = 73/78) of the patients with 51% (n = 40) of those as planned tandem ASCT and 42% (n = 33) as salvage procedure at disease progression. Next, we investigated clinical outcomes including relapsed free survival (RFS) and overall survival (OS) between the two groups. The RFS at 1, 2 and 5 years in the group with sustained MRD negativity (n = 129) was 96% (93–100), 91% (86–96),78% (71–86) compared to only 66% (57–78), 48% (38–60) and 24% (16–37) at 1, 2 and 5 years respectively in the group with persistent MRD positivity (n = 78). Similarly, the OS at 1, 2 and 5 years were 99% (98–100), 96% (93–100) and 85% (79–91) respectively in patients with sustained MRD negativity compared to 88% (82–96), 75% (66–85) and 40% (31–53) in patients with persistent MRD positivity. The median RFS and OS in the group with persistent MRD positivity was 1.6 (1.0–3.2) and 3.8 (3.2–6.3) years, respectively compared to median not reached in sustained MRD negative group. (Figure 1(A), (B)). Looking specifically at the distribution of GEP 70 persistent MRD positivity, HR disease was associated with dismal RFS of 1.6 years and OS of 1 year. Patients with LR disease and persistent MRD positivity had a median RFS and OS of 2.6(1.6–4.8) and 5.2(3.9-NR), respectively (Figure 1(C), (D)). Patients with baseline GEP 70 HR who showed sustained MRD negativity had a median RFS of 6.2 years (1.8-NR) and the median OS was not reached (5.5-NR) (Figure 1(C), (D)). The median RFS and OS were not reached in GEP 70 LR with sustained MRD negativity (Figure 1(C), (D)). In the context of persistent MRD disease, tandem ASCT (HR 0.57, 95% CI 0.25–1.28, p = 0.2) and age failed to meet statistically significance, while ISS stage III disease (HR 2.69, 95% CI 1.13 6.39, p = 0.025), HR GEP70 signature (HR 4.30, 95% CI 1.73–10.7, p = 0.002), GEP subtype MF (HR 5.87, 95%CI 1.61–21.4, p = 0.007) and MS (HR 5.37 95% CI 1.67–17.3, p = 0.005) were independently associated with inferior RFS and OS on multivariate analysis (Tables S3 and S4). We also analyzed 71 patients with persistent MRD positivity and paired BM GEP studies obtained at diagnosis and at the time of progression or relapse. At presentation, the majority (n = 61; 78.2%) of patients had GEP 70 defined LR disease. Overall, among the patients with LR disease at diagnosis, who had serial GEP assessment (n = 61), 10 (16.3%) patients changed from LR to HR GEP70 signature. Altogether, at relapse 32.8% (20/61) were HR GEP 70 (20/61) (Figure S3). The current study indicates for the first time to our knowledge that the outcome of NDMM patients with persistent BM MRD positivity at all assessments resembles that of primary refractory disease; in both circumstances, sequential intensive therapies failed to eradicate residual MRD clone(s).8, 9 Notably, at diagnosis the distribution of FISH-defined HR disease or ISS stage were not different between persistent MRD negative and MRD positive patients, suggesting that persistent MRD positivity confers a poor outcome regardless of these traditional risk factors routinely used in clinical practice. As previously shown, MRD status supersedes IMWG response with no statistically significant difference in RFS and OS in patients who attained CR/VGPR versus PR/SD.10 However, the prognosis of MRD positive patients is worse in the setting of higher stage of the disease (ISS stage) and high-risk disease (GEP 70) consistent with previous studies.6 Recent reports indicate that phenotypic and genomic features of MRD tumor cells show the presence of therapy-induced clonal selection with overexpression of adhesion molecules, integrins and chemokine receptors conferring a survival advantage in the BM microenvironment.11 Recent studies also show that residual MRD especially in the setting of HR disease is associated with acquisition of new mutations conferring increased genomic instability in residual tumor cells.12 Not surprisingly, the HR GEP70 signature drives the poor outcome in this group of patients with RFS and OS of 1 (0.7–1.5) and 1.5(0.91–2.6) years, respectively (Figure 1(C), (D)). In agreement with previous reports, we observed a higher percentage of patients with HR GEP 70 score and a shift to PR with disease progression in patients with LR disease at presentation.13 These interpretations should be viewed cautiously in the context of intra and inter-tumoral and spatial heterogeneity especially in advanced disease.13, 14 On the other hand, patients with GEP 70 LR disease and assigned to CD2 subtype on GEP 70 less frequently changed to a PR subtype and/or HR GEP 70 signature compared to HY and CD-1 subtypes (Figure S3).6, 15, 16 Using serial BM MRD as the only discriminating tool, we were able to identify a group of NDMM patients with dismal clinical outcomes despite intensive transplant-based approach.17, 18 Thus, in the current study persistence MRD positivity clearly trumps traditional risk stratification tools and clinical response assessment and identifies patients who behave like HR GEP70 disease in need for alternative treatment approaches. We acknowledge that this study has several limitations inherent to its retrospective nature including small sample size and heterogenous treatment regimens. The data reported here is reflective of clinical outcome with PI, IMiD, and monoclonal antibody daratumumab-based therapies at relapse, which are FDA approved medications in the relapsed MM setting. Other immunotherapy approaches like T cell directed therapies and antibody drug conjugates should be tested in this setting.19 The authors thank the patients and staff of the Myeloma Center, University of Arkansas for Medical Sciences. The authors declare no potential conflict of interest. The data that support the findings of this study are available from the corresponding author upon reasonable request. Figure S1. Kaplan Meier curves showing overall survival of patients with persistent MRD positivity when stratified based on application of tandem transplants. Figure S2. Kaplan Meier curves showing shows the relapse free and overall survival of patients with persistent MRD positivity stratified by best response at D100 post ASCT. Figure S3. Figure showing the shift in the GEP 70 signature and subtype at relapse in patients with low risk GEP70 at presentation. Figure compares the distribution of GEP 70 subtypes at diagnosis to those at relapse. Table S1. Table comparing the baseline characteristics of a cohort of persistent MRD positivity to sustained MRD negativity. Table S2. Table showing the results of multivariate analysis comparing distribution of the clinical variable between the group with sustained MRD negativity and persistent MRD disease. Table S3. Table showing multivariate analysis of predictors of Progression free survival in group of patients with persistent MRD positivity. Table S4. Table showing multivariate analysis of predictors of overall survival in patients with persistent MRD positivity. 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