Minimal Residual Disease in Multiple Myeloma Patients: Influence on Indicators of Progression Free Survival

Background. Induction, consolidation of response and maintenance therapy are very effective approaches in the treatment of patients with multiple myeloma (MM). However, the majority of patients will inevitably relapse despite achieving progressively higher complete response (CR) rates. Activation of residual clonal plasmatic cells is a cause of relapse disease. Therefore, the assessment of minimal residual disease (MRD) is a strong prognostic factor for progression-free survival (PFS).

Aim. To estimate influence of MRD on PFS indicators in MM patients. Methods. We analyzed 28 patients with MM (median age 56 years, male/female - 1.8:1). 5-color flow cytometry was used for immunophenotyping of bone morrow cells as well as definition of primary tumor cells phenotype and detection of MRD. Such markers as CD38, CD138, CD45, CD19, CD20, CD27, CD56 and CD117 were used to identify clonal plasma cells. In addition, MRD was assessed by FISH analysis in patients with genetic abnormalities; CT-PET carried out to patients with the MRD-negative CR.

Results. Patients had bortezomib- or lenalidomide-based programs of therapy. Autologous stem cell transplantation (ASCT) was carried out in 18 patients. Performing ASCT statistically significantly increased frequency of MRD-negative CR (p<.01). Before ASCT MRD-negative CR was reached in 3/28 (10,7%) patients. After ASCT 9/18 (50,0%) patients were transferred to the MRD-negative group (6/9 patients before ASCT had MRD-positive CR, 1/9 - MRD status did not change, 2/9 - stringent CR was reached). One patient with MRD-negative CR had CT-PET positive specific lesions. 19/28 (67,8%) patients were transferred to the MRD-positive group (9/19 patients had CR, 5/19 - VGPR, 5/19 - PR). The median PFS didn't correlate with ASCT in general and the MRD-positive groups (р>.05). PFS in the MRD-negative group was better than in the MRD-positive group with CR (median was not reached vs median of 63.9 months, respectively; 2-year PFS was 100% vs 77%, respectively) (p=.0048). In addition, we analyzed the influence of CR in the MRD-positive group on PFS. Absence of CR is an inferior prognostic factor and is characterized by decrease of PFS in patients with MRD-positive status. The median PFS in the MRD-positive group with CR was 63.9 months and 26.0 months in the MRD-positive group without CR (VGPR and PR) (p=.049). Genetic abnormalities were detected in 7/26 (26.9%) patients before antimyeloma therapy: t(11;14) - in 5/26 (19.2%), del(13q) - in 3/26 (11.5%), t(4;14) - in 1/26 (3.8%), del(1p) - in 1/26 (3.8%). After treatment patients with CR (MRD-positive and MRD-negative) had normal genetic status by FISH. Only 1/7 patients with MRD-positive PR had residual clone with del(13q).

Conclusion. Performing ASCT influences frequency of MRD-negative CR. The PFS indicators (median and 2-year PFS) were higher in the group of MM patients, who had MRD-negative status of the disease compared to than in the MRD-positive group. The FISH method had low sensitivity in detection of residual clone with genetic abnormalities, especially in patients with CR.