Cytarabine-based mobilisation yields higher CD34+ cell counts than cyclophosphamide regardless of prior daratumumab exposure in multiple myeloma

Introduction Anti-CD38-based quadruplets such as daratumumab-bortezomib-lenalidomide-dexamethasone (D-VRd) or daratumumab-bortezomib-thalidomide-dexamethasone (D-VTd), where lenalidomide is not reimbursed, are the internationally recommended first-line treatment for transplant-eligible myeloma. There is ongoing debate about whether anti-CD38 exposure impairs stem cell collection. Most studies compare daratumumab-containing with non-daratumumab induction whilst keeping the mobilisation strategy constant. None have compared two mobilisation agents against each other in both daratumumab-exposed and daratumumab-naïve patients. Methods We reviewed 66 patients (22 received Ara-C, 44 received CY) who were mobilised at a single centre in Poland between 2018 and 2024. No patients received plerixafor. Results Patients who were mobilised with Ara-C collected more CD34+ cells than those who received CY, with a median of 12.6 (IQR 9.1–15.9) versus 7.7 (4.9–12.1) ×10⁶/kg (p=0.005), with comparable apheresis sessions. Previous D-VTd treatment did not reduce the overall yield (p=0.43). The benefit of Ara-C persisted in the D-VTd subgroup, despite heavy confounding between induction and mobilisation choice. Discussion This is the first direct comparison of Ara-C and CY in the daratumumab era. Ara-C-based mobilisation was associated with higher CD34+ yields than CY in a plerixafor-free setting. The apparent advantage in D-VTd-treated patients is exploratory and requires prospective confirmation.