In contrast, mobilization with chemotherapy (mostly cyclophosphamide) in addition to G-CSF has been shown to improve PBPC collection yield and reduce mobilization failure rates in comparison to G-CSF alone. Limited retrospective data suggest that cyclophosphamide may overcome the effects of prior lenalidomide exposure on PBPC mobilization in MM patients. Cyclophosphamide doses employed for mobilization of PBPC in MM patients in most reports have ranged from 1 gm/m2 up to 7 gm/m2. Several studies have assessed the relative impact of cyclophosphamide dose-intensity on PBPC mobilization in myeloma patients treated with conventional chemotherapy regimens. In general PBPC mobilization with high-dose cyclophosphamide (HD-CY) (7 gm/m2) plus G-CSF was found to be significantly more toxic, when compared to intermediate-dose cyclophosphamide (ID-CY) (3-4 gm/m2) and G-CSF, without any convincing evidence of superior efficacy. Studies comparing mobilization with ID-CY plus G-CSF with low-dose cyclophosphamide (LD-CY) (1-2 gm/m2) plus G-CSF, reported higher total CD34+ cell yield with ID-CY, but at the cost of higher toxicity. However, no significant difference in mobilization failure rates between the ID- and LD-CY mobilization has been reported. But these data might not be applicable to MM treated in the era of novel agents. Hamadani et al. compared the efficacy and toxicity of PBPC mobilization with G-CSF and either ID-CY or LD-CY, in MM patients receiving only novel induction regimens, and reported a more robust PBPC mobilization and significantly reduced the rates of mobilization failure with ID-CY in MM patients receiving modern inductions. Within the context of stem cell mobilization in MM patients treated with novel inductions, it appears that ID-CY and G-CSF may have a favorable risk/benefit ratio and can be considered a regimen with an optimal dose-intensity in order to assess the efficacy of novel mobilization regimens against cyclophosphamide-based mobilizing strategies. But these single center observations merit confirmation in large, multicenter datasets.