[Role of minimal residual disease detection by multiparameter flow cytometry in newly diagnosed multiple myeloma: an analysis of 106 patients].

Objective: To assess the feasibility and prognostic value of the minimal residual disease (MRD) evaluated by multiparameter flow cytometry (MFC) in the newly diagnosed multiple myeloma (MM) patients of China. Methods: Clinical data of 106 consecutively newly diagnosed MM patients with MRD data were retrospectively analyzed in a single center in China from June 2013 to June 2015. Results: ① Of 106 patients, 48 (45.3%) achieved MRD negativity. The median time to MRD-negative was 3 months. More patients undergoing autologous stem cell transplantation (ASCT) achieved MRD negativity compared with non-ASCT patients (62.2% vs 36.2%, χ (2)=6.536, P =0.011). ② Of 48 patients in complete remission (CR), 7 (14.6%) was MRD positive, 5 of them showed disease progression (PD) during the follow-up, and 3 died. The median progression free survival (PFS) was 19 months, and the median overall survival (OS) was 28 months, both were significantly shorter than the CR patients with MRD-negative ( P <0.05). ③At a median follow-up of 38 months, MRD-negative patients showed significantly superior outcomes compared with MRD positive ones, the PFS was not reach versus 17 months and the OS was not reach for both ( P <0.001). Patients were grouped into 4 categories according to their MRD levels: 1% or higher, 0.1% to less than 1%, 0.01% to less than 0.1%, or negative. It showed that the outcomes (PFS and OS) tended to be improved along with the tumor depletion. ④ Multivariate prognostic analysis showed that MRD was a powerful independent prognostic factor for PFS[ HR =0.133 (95% CI 0.062-0.288) , P <0.001] and OS[ HR =0.156 (95% CI 0.050-0.484) , P =0.001]. According to MRD and cytogenetics, the patients were classified into 4 groups. High risk patients with MRD negative presented a significantly better outcome than high risk patients with MRD-positive, and a similar one to the standard risk patients with MRD-negative. Conclusions: MRD negativity by MFC was more popular in MM patients undergoing ASCT. MRD was an independent prognostic factor in MM. And the prognosis of MM patients can be stratified according to the level of MRD. MRD-negative patients with high risk cytogenetics presented a similar outcome to the standard risk ones. MRD by MFC should therefore be considered more widely applied in the clinic.