Factors predicting peripheral blood stem cell (PBSC) mobilization with plerixafor in multiple myeloma patients who had inadequate mobilization with G-CSF.

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Background & Aim Autologous transplant utilizing G-CSF mobilized peripheral blood stem cells (PBSC) is considered standard practice for eligible multiple myeloma (MM) patients. G-CSF is often utilized as the preferred agent and Plerixafor added if there is inadequate PBSC mobilization with G-CSF alone. To the best of our knowledge, there are no studies predicting the response of the poor mobilizers to plerixafor. Methods, Results & Conclusion METHODS MM patients undergoing PBSC collection in our institution were retrospectively studied. Patients received 10 μg/kg G-CSF SQ daily. Stem cell collection started on day 4 (after 3 doses of G-CSF) if blood CD34 count on day 4 was at least 10 /μL (Good mobilizer). If not (Poor mobilizer), patients received 240 μg/kg plerixafor SQ and another dose of G-CSF on day 4 followed by collection starting day 5. Complete blood count was measured before G-CSF (day 0) and on days +2, +3, and +4, . and CD34 count on day +5 . Based on day +5 CD34 count patients were categorized into two groups; Above Median (AM) with CD34 count above median or Below Median (BM; CD34 = Results 73 patients were studied. Median age 61 yr, (39-74), 44 (61%) were men. Median CD34 count on day +5 was 41.9/µL, 37 were in BM and 36 in AM groups. Disease duration prior to mobilization strongly correlated with plerixafor response (25.9m v 15.1m in BM v AM, p=0.02) . Mean day 0, day 2 and day 3 platelet count was higher in AM compared to BM (236 v 192,P =0.0075 on day 0, 182 v 148, p=0.0003 on day 2, and 195 v 152 p=0.0001 on day 3). Platelet count dropped from day 0 to day 2 in the whole cohort but more so in the BM compared to AM group (mean drop 20.7% v 15.6%, p=0.04) . Day 0 ANC was not different (2.7 v 2.5,P =0.47) but ANC on day 2 was higher (25.9) in AM compared to 18.6 in BM group, p=0.007. Low CD34 count on day 3 prior to plerixafor administration strongly correlated with plerixafor response (4.5 v 6.7 in BM v AM, p=0.0006) Discussion We found that disease duration, day 0 and day + 2 platelet counts, day +2 ANC and day +3 CD34 counts were sensitive predictors for Plerixafor response. Also we observed that extent of platelet and ANC count change between day 0 and day +2 were predictors of plerixafor response.. These findings have implications for choosing mobilization strategies for patients who have inadequate CD34 mobilization with G-CSF alone.