Current strategies for the management of autologous peripheral blood stem cell mobilization failures in patients with multiple myeloma

Multiple myeloma (MM) is the leading indication of autologous hematopoietic stem cell transplantation (AHSCT) worldwide. The collection of PBSCs is the essential step for AHSCT. The limits for minimum and optimum CD34⁺ cells collected have been accepted as 2 × 10⁶ /kg and ≥4 × 10⁶ /kg for single AHSCT; 4 × 10⁶ /kg and ≥8-10 × 10⁶ /kg for double AHSCT. Despite the success of conventional methods for PBSC mobilization in MM, mobilization failure is still a concern depending on patient age, duration of disease, and the type of induction therapy. By definition, "proven poor mobilizer" is the occurrence of mobilization failure (CD34+ cell peak <20/µL peripheral blood) after adequate preparation (after 6 days of G-CSF 10 µg/kg body weight alone or after 20 days of G-CSF >5 µg/kg body weight following chemotherapy) or a CD34+ cell yield of <2.0 × 10⁶ /kg body weight after three consecutive apheresis. "Predicted poor mobilizer" involves (1) a failure of a previous collection attempt OR (2) a previous history of extensive radiotherapy or full courses of therapy affecting mobilization OR (3) the presence of at least two of the following features: advanced disease (>2 lines of chemotherapy), refractory disease, extensive bone marrow involvement or cellularity of 30% at the time of mobilization or age >65 years. This article aims at discussing the risk factors for mobilization failure in the era of novel antimyeloma drugs, defining the poor mobilizer concept and summarizing the current and future strategies for the prevention and management of mobilization failures in MM.