The prognostic value of multiparameter flow cytometry minimal residual disease assessment in relapsed multiple myeloma | Haematologica

摘要

Achieving deep levels of remission is one of the prerequisites to reach long-term survival in solid tumors and hematologic malignancies, and this has also been proved in newly diagnosed multiple myeloma (MM) patients, particularly in the era of novel agents.1–3 Accordingly, both the Spanish and UK groups have shown the prognostic value and clinical relevance of minimal residual disease (MRD) monitoring by multiparameter flow cytometry (MFC) in both newly diagnosed transplant candidates and elderly MM patients treated with novel agents.4–6 However, the value of the depth of response in the relapse setting has been subject to far less investigation than in the up-front setting.7–11 In fact, there are few data exploring different outcomes between patients achieving very good partial response (VGPR) or complete response (CR) with salvage therapy,7–11 and there is no information regarding the prognostic value of achieving immunophenotypic or molecular responses at relapse. If MRD-negativity translated into superior outcomes, like those observed in newly diagnosed patients, then it could become a desirable end point for clinical trials exploring new drugs for relapse/refractory patients.In the present study, we focused on a total of 52 patients who after clinical relapse achieved CR with salvage therapy. Patients were divided into two categories: 21 rescued with novel agents followed by allogeneic stem cell transplantation (alloSCT; n=21), and 31 patients rescued and achieving CR with novel agents (in all except 6) followed or not by autologous stem cell transplantation (autoSCT) (11 and 14 cases, respectively).All samples were collected after informed patient consent according to the local ethical committees and the Declaration of Helsinki protocol. Median follow up was 2.7 years (32 months). MFC studies were performed on bone marrow (BM) samples using 4-color monoclonal antibody combinations (FITC/PE/PerCPCy5.5/APC), as described elsewhere.4,5,12 Plasma cells (PCs) were initially identified on the basis of strong CD38 expression and intermediate side scatter signals; discrimination between clonal and normal PCs was performed by the recognition of aberrant phenotypic expression profiles such as simultaneous downregulation of CD19 and CD45, with or without overexpression of CD56. For patients in whom CD45 or CD19 was positively expressed, lack of CD19 or CD45, respectively, dim CD38 intensity and/or bright CD56 staining (equal or higher than that of natural killer cells) allowed identification of clonal PCs in the vast majority of cases; in selected patients (n=7), CD56 was replaced by CD28, CD81 or CD117 since these markers were known to be more informative according to the base-line phenotypic evaluation. Data acquisition was performed in FACSCalibur and FACSCantoII flow cytometers (Becton Dickinson Biosciences, BDB, San Jose, CA, USA) using the FACSDiva 6.1 software (BDB), and a 2-step acquisition procedure allowing for a minimum of 2×105 leukocytes/tube to be selectively stored. Data analysis was performed using the Paint-a-Gate (BDB) and the Infinicyt software (Cytognos SL, Salamanca, Spain). Patients were defined as being MRD-negative when less than 20 clonal PCs were detectable by MFC, at a sensitivity level of 10?4. Time-to-progression (TTP) was measured from the moment of MRD assessment to the date of progression or last visit. Curves were plotted by the Kaplan-Meier method, and the log rank test was used to estimate the statistical significance of differences observed between curves. The Cox proportional hazards model was used to estimate hazard ratios (HR) and 95% confidence intervals (95%CI), as well as to perform a multivariate analysis including patients’ MRD status (dichotomized into negative/positive), type of treatment (dichotomized into yeso): autoSCT, novel agents; proteasome inhibition, immune modulators, as well as the event of extramedullary relapses (dichotomized into yeso). The X2 test was used to estim