Background: To promote the judicious use of plerixafor (PLX), our institution implemented an original algorithm for autologous stem cell mobilization in combination with on-demand PLX use (PLX-A), in which PLX is administered to patients with preceding-day peripheral blood CD34-positive cell (PBCD34+) counts below 20 cells/μl and therefore at risk of poor mobilization.

Methods: Twenty-five cases in the pre-PLX-A period and 31 cases in the post-PLX-A period were included. Rates of successful one-day collection, namely with CD34+yields ≥ 2×10⁶/kg, in these two periods were compared. Further, associations of success rates with the preceding-day PBCD34+measurements and PLX administration among the post-PLX-A cases were retrospectively investigated.

Results: Successful one-day collection rate was significantly higher in the post-PLX-A cases than in the pre-PLX-A cases (48% vs 77%, p=0.03). Among 14 post-PLX-A cases with PBCD34+measurement, success rates of nine non-PLX-administered and five PLX-administered cases were 100% and 80%, respectively, while that of 15 post-PLX-A cases with neither PBCD34+measurement nor PLX administration was 60%. The PLX-A was not applied to three cases, although all of these cases had successful one-day collection.

Conclusions: The PLX-A was useful for improving the successful one-day collection rate. However, six of seven post-PLX-A cases with unsuccessful one-day collection did not have PBCD34+measurement, indicating underestimation of poor mobilization risk. These results suggest the need to revise the current PLX-A.