Phase 1 Study of Bortezomib, Fludarabine, and Melphalan, With or Without Total Marrow Irradiation, as Allogeneic Hematopoietic Stem Cell Transplant Conditioning for High-risk or Relapsed/Refractory Multiple Myeloma

We conducted a phase 1 study of a conditioning regimen with or without total marrow irradiation (TMI) before allogeneic hematopoietic stem cell transplantation for patients with high-risk or refractory multiple myeloma.Eighteen patients were enrolled on one of 2 strata. Patients with no prior radiation received TMI (900 cGy), fludarabine (FLU), and melphalan (MEL) conditioning, with bortezomib added in the second cohort (stratum I). Patients with prior radiation received FLU, MEL, and bortezomib, without TMI (stratum II).Eight patients were enrolled in the TMI arm (stratum I). One of 3 patients in cohort 1 experienced dose-limiting toxicity (DLT), which led to the expansion to 3 more patients with no DLT. Cohort 2 enrolled only 2 patients due to low accrual, with bortezomib, added at 0.5 mg/m2; neither experienced DLT. Nine patients were enrolled in the non-TMI arm (stratum II). Three patients were enrolled in cohort 1 (bortezomib 0.5 mg/m2) and none experienced DLT. Three were enrolled in cohort 2 (bortezomib 0.7 mg/m2), and 1 experienced DLT; therefore, the cohort expanded to 3 more patients. One more patient experienced DLT. Median overall survival on strata I and II was 44.5 months (95% CI: 1.73-not reached) and 21.6 months (95% CI: 4.1-72.7), respectively. Median progression-free survival on strata I and II was 18.1 months (95% CI: 1.73-not reached) and 8.9 months (95% CI: 2.7-24.4), respectively.TMI 900 cGy, FLU, and MEL are considered feasible as conditioning for allogeneic stem cell transplantation and may warrant further investigation due to favorable response rates and survival.