Molecular Level of Minimal Residual Disease in Bone Marrow Before High-Dose Therapy and Autologous Stem Cell Transplantation Is a Prognostic Parameter in Patients with Multiple Myeloma.
Authors: Fenk Roland , Korthals Mark , Sehnke Nina , Bruns Ingmar , Czibere Akos , Zohren Fabian , Safaian Nancy , Dienst Ariane , Ruf Leilani , Neumann Frank , Haas Rainer , Kronenwett Ralf , Kobbe Guido 
Published: April 2020

Abstract
Background: Using real-time quantitative (RQ) PCR we recently (Haematologica89,2004) identified a prognostic cut-off level of residual clonotypic cells in the bone marrow of patients with multiple myeloma before high-dose therapy (HDT) and autologous peripheral blood stem cell transplantation (PBSCT). In this study we validate this report with a larger number of patients.
Patients and Methods: Bone marrow samples of 68 patients with stage II/III multiple myeloma and heavy chain disease were obtained at the time of diagnosis and after induction therapy and stem cell collection but before single HDT and autologous PBSCT. Sequencing of the patient specific immunoglobulin heavy chain (IgH) locus was successful in 51 patients (75%). For 49 patients (72%) RQ-PCR using allele-specific oligonucleotide (ASO) Taqman probes together with LightCycler technology could be established with a sensitivity of 10−4 to 10−6 and linear amplification conditions. The proportion of clonotypic cells was assessed as IgH / 2 beta-actin ratio in percent. Patients were divided in two prognostic groups by a threshold level of 0.03% clonotypic cells.
Results: The median level of residual tumor cells in bone marrow of all patients at the time before transplantation was 0.05% (range: 0–21%). Time to progression (TTP) from the time of diagnosis of patients in the ¨good¨ prognostic group (n = 21) was 51 months and significantly (p = 0.002) longer in comparison to 20 months of patients with a pre-transplantation minimal residual disease level of more than 0.03% in BM (n = 28). Overall survival (OS) of patients within the ¨good¨ prognostic group was also significantly prolonged (median OS: not reached versus 46 months, p = 0.03). Univariate analysis also revealed kind of maintenance / consolidation therapy (thalidomide, interferon, reduced intensity conditioning (RIC) allogeneic transplant) and cytogenetic banding analysis as prognostic markers for TTP. For OS kind of maintenance therapy, cytogenetic abnormalities, ISS stage, CRP and LDH levels were of prognostic relevance. In multivariat analysis grouping by pre-transplantation MRD level was an independent prognostic factor for either TTP and OS.
Conclusion: Quantitative molecular assessment of pre-transplantation tumor level in the bone marrow is an independent prognostic parameter for TTP and OS of patients with multiple myeloma. This finding has two controversial implications. One conclusion could be, that induction therapy should be continued and intensified e.g. with novel agents until a low MRD level is achieved. An alternative conclusion is, that a low tumor burden after induction therapy may be a surrogate parameter for chemosensitive disease, which makes patients more susceptible for high-dose chemotherapy. Therefore, further MRD studies are needed to answer this important question.