The prognostic relevance of minimal residual disease (MRD) in patients with multiple myeloma is still an open question. In bone marrow, the level of residual myeloma cells is associated with treatment outcome, but the role of clonotypic cells in the peripheral blood (PB) for the prognosis of patients is not identified yet. In this study, we retrospectively analyzed MRD by quantitative real-time IgH-PCR (IgH-qPCR) in the PB of 42 patients undergoing high-dose therapy followed by autologous PB stem cell transplantation as first-line therapy for multiple myeloma. The MRD level of PB samples was in median 40-fold lower than in bone marrow samples, collected on the same day, with a wide intra- and interindividual variation (range, .4- to 4628-fold). The presence or absence of detectable MRD levels in PB did not correlate with the serological remission status. Still, patients with negative PCR results in PB 3 months after high-dose therapy and PB stem cell transplantation had lower International Staging System stage (P = .01), lower levels of β2-microglobulin (P = .02), higher hemoglobin levels (P = .01), and a prolonged event-free (median, 15 versus 4 months; P = .004) and overall (median, 52 versus 17 months; P = .03) survival. Importantly, by sequential monitoring of clonotypic cells in PB, in 19 of 29 patients (66%) with progressive disease, an increase of the 2IgH/β-actin ratio of at least 1 log step could be detected in median 4 months (range, .8 to 13 months) before the relapse was diagnosed on the basis of the European Group for Blood and Marrow Transplantation criteria. These patients with a molecular relapse in PB before a serological relapse had a significantly shorter overall survival than other patients (median, 17 months versus median not reached, P = .02). In conclusion, IgH-qPCR is a sensitive technique for the detection of clonotypic cells in PB, which precede clinical relapse. Future studies are needed to evaluate whether these circulating tumor cells play a role in promoting disease recurrence.

The prognostic relevance of minimal residual disease (MRD) in patients with multiple myeloma is still an open question. We measured MRD levels in bone marrow (BM) samples of 53 patients treated with high-dose therapy (HDT) and autologous peripheral blood stem cell transplantation using real-time quantitative (RQ)-IgH-PCR with allel-specific oligonucleotide probes. We identified a prognostically relevant threshold level of 0.2% 2IgH/β-actin ratio in the BM before HDT. Twenty-six patients with MRD levels below this value were termed as the "low-MRD group," whereas 27 patients with levels above this threshold were allocated to the "high-MRD group." Median event-free-survival (EFS) in the low-MRD group was significantly (P = .001) longer than in the high-MRD group with 35 versus 20 months, respectively. Overall survival (OS) within the low-MRD group was also significantly longer with 70 versus 45 months (P = .04). Using multivariate analysis, we found that the pretransplantation MRD level was an independent prognostic factor for EFS (P = .003) and OS (P = .05). Further, EFS of patients in the high-MRD could be improved (P = .005) when they achieved a low MRD level after HDT. In conclusion, measuring MRD is of prognostic relevance in patients with MM, and low MRD levels should be a goal of treatment.

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.