(PA-443) Lenalidomide Duration during Induction Does Not Affect Stem Cell Mobilisation, A Real-World Study with G-CSF and Pre-emptive Plerixafor

Stem cell collection is typically recommended within 4 months of lenalidomide-based induction in multiple myeloma due to concerns over impaired mobilisation with prolonged lenalidomide exposure. However, in resource-limited settings, delays in ASCT are common due to financial constraints and limited access to cryopreservation.In this context, it becomes imperative to determine whether extended lenalidomide exposure impact stem cell mobilisation when G-CSF and pre-emptive plerixafor are used.

Methods: We retrospectively reviewed records of 81 multiple myeloma patients who underwent ASCT between January 2015 and December 2024. Mobilisation was performed with G-CSF (10 mcg/kg), and plerixafor was added if Day-4 peripheral blood CD34+ count was < 10 cells/µL. A Day-5 yield target of >2×10⁶ CD34+ cells/kg was set. Patients were grouped based on lenalidomide exposure: ≤4 months (short-exposure, SE) and >4 months (long-exposure, LE).

Results: Median age was 55 years (IQR: 47.5–60), with younger patients in the LE group (median: 54 vs. 60 years; p = 0.01). Median induction duration was 11 months (IQR: 4–14), with a median lenalidomide exposure of 6 months (IQR: 4–8.25). Fifty-eight patients (72%) were in the LE group. Median Day-4 peripheral blood (PB)CD34+  cell counts were similar between groups (LE = 4.64/µL vs. SE = 5.45/µL; p = 0.27). Day-4 subcategories showed comparable proportions with < 5 cells/µL (48% vs. 55%), 5–10 cells/µL (15.5% vs. 23%), and >10 cells/µL (36.2% vs. 22%; p = 0.59). Plerixafor use was comparable (59% LE vs. 59% SE; p = 0.99). Day-5 median CD34+ yields were similar (LE = 5.12×10⁶/kg vs. SE = 3.88×10⁶/kg; p = 0.14), and the need for >1 apheresis session was not significantly different (LE = 13.8% vs. SE = 27.3%; p = 0.13). In the LE group, 2 patients failed to achieve >2×10⁶/kg yield; none failed in the SE group. Among LE patients, 60% achieved >4×10⁶/kg compared to 36% in the SE group (p = 0.39). Lenalidomide dose, analyzed both as nominal (10 mg, 15 mg, 25 mg) and binary (≤15 mg vs. >15 mg), was not significantly associated with impaired stem cell mobilisation. Patients receiving higher doses ( >15 mg) had comparable Day-4 CD34+ counts and Day-5 yields. Patients < 50 years had higher median CD34+ yield (5.99 vs. 3.83×10⁶/kg; p = 0.02), and the association remained significant after adjusting for exposure duration and dose (p = 0.03). Pre-transplant disease status also predicted stem cell mobilisation; those with ≥PR had higher median yield (5.2 vs. 3.1×10⁶/kg; p = 0.04). Among patients receiving Dara-VRD, there was no significant difference in mobilisation kinetics; however, two-thirds required plerixafor.

Conclusions: Prolonged lenalidomide exposure ( >4 months) and variation in lenalidomide dose did not adversely affect stem cell mobilisation outcomes when G-CSF with pre-emptive plerixafor was used.