Pre-Transplantation Level of Minimal Residual Disease Detected by Quantitative Real-Time IgH-PCR Is a Prognostic Parameter in Patients with Multiple Myeloma.

Background: High-dose chemotherapy with autologous stem cell transplantation has improved outcome and survival of patients with multiple myeloma. However, the majority of patients suffer from relapse. Using real-time quantitative (RQ) PCR we have shown before (Haematologica 89,2004) that the amount of residual tumor cells in the bone marrow of patients before transplantation is of prognostic relevance. In this study we evaluated in a larger group of patients with multiple myeloma whether a pre-transplantation level of clonotypic cells in the bone marrow is predictive for time-to-progression (TTP) and overall survival (OS). Further, we compared results with known prognostic factors.

Patients and Methods: Bone marrow samples of 19 patients with stage II/III multiple myeloma were obtained after induction therapy but before transplantation. Immunoglobulin heavy chain (IgH) RQ-PCR using patient-specific Taqman probes was performed to quantify pre-transplantation tumor levels. The proportion of clonotypic cells was assessed as IgH/2 beta-actin ratio in percent. Medical records of patients were reviewed for prognostic factors and outcome.

Results: The median level of residual tumor cells in bone marrow of all patients at the time before transplantation was 0.3 %. At 23 month median follow-up after transplantation the median TTP and OS in our study were 14 and 36 month, respectively. The threshold level of 0.03% clonotypic cells identified two prognostic groups (p<0.0001, log rank). Twelve patients in the bad prognostic group had an early relapse with a median TTP of 9 month (range: 3 – 17 month). All patients in the good prognostic group (n=7) had ongoing remissions after a median follow-up of 24 month (range: 13–44 month). Univariat analysis was performed including other prognostic factors at the time before transplantation such as cytogenetic abnormalities, beta2-microglobulin, hemoglobulin, platelet count, LDH, CRP, serum albumine and age. Besides the pre-transplant level of minimal residual disease, CRP level was predictive for TTP. In multivariat analysis using a step-wise cox regression model grouping by pre-transplantation tumor level was the only prognostic factor for TTP (p = 0.05). Moreover, low pre-transplantation tumor levels also showed a trend for a better OS, but in multivariat analysis only normal cytogenetics were predictive for a superior outcome (p = 0.03).

Conclusion: Quantitative molecular assessment of pre-transplantation tumor level in the bone marrow is an independent prognostic parameter for the progression-free survival of patients with multiple myeloma and thus helps to guide therapeutic interventions