Biomarkers for Predicting Long-Term Disease Control in Transplant-Ineligible Multiple Myeloma Patients: The Presence of an MGUS- like Signature Is the Most Relevant Predictor

Introduction: Disease control at five years would be a desirable endpoint for elderly multiple myeloma (MM) patients; however, the percentage of cases reaching this objective as well as the biomarkers to predict it, are not well defined.

Objective and design: In order to gain further insight about long-term disease control (>5 years progression-free) in elderly MM we have analyzed a homogeneous population of 435 newly-diagnosed transplant-ineligible (TNE) patients enrolled in two consecutive Spanish clinical trials (GEM2005MAS65, GEM2010MAS65), that included both proteasome inhibitors and immunomodulatory drugs.

Results: Amongst the 435 patients included in this post-hoc study, only 18.8% remained alive and progression-free after five years of initiating treatment. Noteworthy, in these patients the overall survival (OS) rate at 10-years was 69.4%, as compared to 11.4% for those patients progressing during the first five years (p< 0.001). Baseline variables significantly associated with long-term progression free survival in the univariate analysis were younger age, ISS 1, R-ISS 1, hemoglobin ≥ 12g/dl, normal LDH, and standard-risk cytogenetic abnormalities and the presence of a monoclonal gammopathy of unknown significance (MGUS)-like immunophenotypic profile in the bone marrow. Complete responses (CR) and minimal residual disease (MRD) negativity were also associated with long-term progression free survival. In the multivariate analysis, an hemoglobin level ≥12g/dl (OR 2.61; 95% CI 1.47 - 4.61, p=0.001) and a MGUS-like immunophenotypic profile in the bone marrow (OR 3.33; 95% CI 1.30 - 8.54, p=0.002) were the two baseline variables significantly and independently associated with a higher probability of long-term disease-free survival. When the depth of response (including MRD) was included in the logistic regression model, Hb level ≥12g/dl (OR 2.18; p=0.010) and the MGUS-like signature (OR 4.99, p<0.001) retained their independent predictive value along with the achievement of MRD-negativity (OR 4.09, p<0.001).

Focusing on the 24 patients with an MGUS-like signature (based on the automated immunophenotyping analysis of the relative frequency of BM plasma cells (PCs) plus the percentage of clonal and normal PCs within the whole BM PC compartment), 50% percent of these patients displayed a long-term disease-free survival, as compared to only 17.5% of the remaining MM patients. The median OS for patients with MGUS-like signature was 90.2 months as compared to 62.6 for the MM-like patients. Most MGUS-like patients (90.5%) achieved a favorable response (10 complete response (CR) and 9 very good partial response (VGPR)). No differences in outcome were observed between VGPR and CR cases (p-value for OS 0.87) among MGUS-like patients.

Conclusions: This study revealed that despite the usage of former novel agents, the probability of disease control at five years is still restricted to a small fraction (18.8%) of transplant-ineligible patients that achieve remarkable rates of long-term OS. Here, we identify that the combination of three biomarkers (normal Hb, MGUS-Like signature and MRD negativity) can help todefine elderly MM patients achieving long-term disease control. Our results highlight the presence of an MGUS-like signature in the bone marrow at diagnoses as the most powerful predictor for long-term disease free survival, and could be incorporated in clinical practice in order toimprove the prognostic information given to our patients.