PB2185: MINIMAL RESIDUAL DISEASE AND THE NUMBER OF CD34+ CELLS CIRCULATING IN THE PERIPHERAL BLOOD OF MULTIPLE MYELOMA PATIENTS ON THE DAY OF THE FIRST SESSION OF LEUKOCYTAPHERESIS DURING AUTOGRAFT HARVESTING

Abstract

Background: The efficiency of autograft harvesting, i.e. the number of CD34+ cells in terms of the patient’s weight is determined by factors characterizing the intensity of the mobilization regimen, describing the type and duration of therapy preceding the collection of hematopoietic stem cells (HSC), and also assessing the activity of the disease. The significance of the volume of residual myeloma cells on the quantitative composition of the autograft of patients with multiple myeloma (MM) is not clear. Therefore, the question of the appropriateness of choosing the appropriate mobilization regimen depending on the status of minimal residual disease (MRD) remains open. Aims: To evaluate the possible influence of MRD status on the mobilization HSCs from the bone marrow into the peripheral blood in patients with MM. Methods: A retrospective analysis of the results of HSC mobilization in 64 patients with MM was performed. Mobilization of HSCs was carried out by regimens with introduction of cyclophosphamide 3 g/m/2 (n=14), vinirelbine 35 mg/m/2 (n=30), granulocyte colony-stimulating factor (G-CSF) (n=16) and plerixafor (n=4). When using cyclophosphamide, vinorelbine and plerixafor, patients additionally prescribed G-SCF. The efficiency of mobilization was assessed by the number of CD34+ cells circulating in one mkL of peripheral blood on the day of the first session of leukocytapheresis. To initiate leukocytoapheresis, this indicator had to be at least 20. Thus, cases of unsuccessful mobilization were excluded from the analysis. The status of MRD was assessed by the results of flow cytometry performed before the start of the mobilization regimen. An indicator of >0,01% was considered positive. Results: There were 20 and 44 patients with MRD (-) and MRD (+) status in the study, respectively. The number of CD34+ cells circulating in the peripheral blood on the day of the first session of leukacytapheresis in the patients in the group did not differ: 154 and 88.5/mkL, respectively; p=0.164. The difference was also not significant depending on the mobilization regimen used, despite the trend towards a negative effect of less intensive courses in the case of a significant volume of residual cells. So if in the group of cyclophosphamide CD34+ cells in 1 mkL of blood of patients with MRD (-) status and MRD (+) status were 97 and 90, respectively; p=0.540, then when prescribing vinirelbine 276 and 109, respectively; p=0.116 and 117 and 47, respectively, with the introduction of G-SCF; p=0.173. Summary/Conclusion: The potential of the used mobilization regimens does not depend on the MRD status of patients with MM. However, the trend towards a decrease in the number of CD34+ cells circulating in the peripheral blood on the day of the first session of leukacytapheresis with the use of less intensive schemes (G-CSF, vinorelbine with G-CSF) gives reason to take into account the status of MRD when choosing a mobilization regimen.