Autologous stem cell transplantation (ASCT) can be applied to consolidate first remission (CR1) in favorable/intermediate-risk acute myeloid leukemia (AML) patients. [1][2] However, up to 20% of AML patients in CR1 fail to mobilize a sufficient number of peripheral blood stem cells (PBSC). 3 We evaluated safety and effectiveness of adding plerixafor to continued G-CSF stimulation in 5 AML patients in CR1, who had failed to mobilize at least 10 CD34 + cells/mL in the peripheral blood. The patients received a single dose of 24 mg plerixafor intravenously 4 hours before apheresis. Subsequent PBSC collection was successful in all patients enabling them to proceed to ASCT, and all autografts were molecularly minimal residual disease (MRD)-negative. These data suggest that plerixafor added to G-CSF stimulation is effective in AML patients with otherwise failing stem cell PBSC mobilization.In AML patients in CR1, high CD34 + cell counts harvested in a single apheresis or high percentages of CD34 + cells in the autografts are associated with adverse outcome. 4 We and others demonstrated that high numbers of peripheral circulating CD34 + cells at PBSC collection predicted higher relapse risk, whereas delayed hematologic recovery after ASCT was associated with better survival rates. [5][6][7][8] Accordingly, a decreased mobilization potential after induction chemotherapy can indicate a favorable course in AML patients, in contrast to, for example, myeloma patients undergoing high-dose chemotherapy (HDCT)/ASCT. [5][6][7]9 Mobilization failure in AML patients in CR1 is so far poorly studied, and subsequent alternative strategies are limited to bone marrow (BM) harvesting with all its inconveniences. Moreover, physicians are reluctant to use the rescue CXCR4 antagonist plerixafor in AML patients given the possible mobilization of residual leukemic stem cells and the possibility to harvest mobilized leukemic cells. 10 However, this conclusion is not based on clinical data in this situation. Accordingly, we investigated in this study the safety and effectiveness of adding rescue plerixafor in AML patients, which otherwise would have failed stem cell mobilization.We studied 5 patients with therapy-naïve de novo AML, who received 2 cycles of induction chemotherapy at the University Hospital of Bern. All patients had achieved CR after the first induction cycle and were planned for consolidation with HDCT/ ASCT based on their genetic risk profiles (Table 1). The second induction cycle comprised cytarabine and daunorubicin in all patients, and when BM assessment on day 18 confirmed remission, G-CSF was started on the first day of neutrophils rising >0.5 G/L. Stem cell collection was planned on the first day of peripheral circulating CD34 + cells exceeding 20/mL. However, all 5 patients failed to achieve at least 10/mL despite continued G-CSF stimulation and were considered mobilization failure.According to European Leukemia Net criteria, 4 patients had favorable and 1 patient had intermediate risk. 11 Four patients showed mutations ...

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