Bortezomib Given in Sequence with Anthracycline and Thalidomide-Containing Regimens Does Not Adversely Affect Stem Cell Mobilization and Engraftment in Patients with Multiple Myeloma Undergoing Autologous Hematopoietic Stem Cell Transplantation.

Bortezomib (VELCADE^®) is a selective inhibitor of the 26S proteasome proven to be safe and effective in the treatment of relapsed or refractory multiple myeloma (MM). While high-dose chemotherapy with autologous hematopoietic stem cell transplant (AHSCT) remains the standard of care, there is considerable interest in incorporating bortezomib into the initial treatment of MM. However, the role of bortezomib in frontline therapy for MM will depend in part on its effects on subsequent stem cell mobilization and engraftment. We conducted a pilot study of bortezomib administered pretransplant followed by high-dose melphalan with AHSCT. Two cycles of bortezomib 1.3 mg/m² were administered on days 1, 4, 8, and 11 of a 21-day treatment cycle. One week after the last dose of bortezomib, stem cell mobilization was initiated by administering filgrastim 10 mcg/kg/day subcutaneously on consecutive days until stem cell harvest was completed. Stem cell collection began on day 5 of filgrastim via large volume apheresis (20 L/day) performed daily until a minimum of 2.5 x 10⁶ CD34⁺ cells/kg were collected. Patients were subsequently admitted to the hospital for high-dose melphalan 100 mg/m²/day x 2 days followed by reinfusion of peripheral blood stem cells 48 hours later. Sargramostim 250 mcg/m²/day subcutaneously was administered starting day +1 post-transplant and continued until the absolute neutrophil count (ANC) ≥ 1,500/mm³ for 2 consecutive days. To date, 23 of a planned 40 patients have been enrolled in this study with 19 patients having completed their initial therapy with bortezomib followed by AHSCT. Patient population consists of 16 male and 7 female patients with the median age at diagnosis of 58 years (range 38–68). Myeloma characteristics at diagnosis were as follows (number of patients): IgG (16), IgA (7) with stage II (9) or stage III (14) disease. Prior to receiving bortezomib, 11 patients were treated with VAD (vincristine, Adriamycin and dexamethasone) or DVd (Doxil, vincristine and dexamethasone), 5 patients with thalidomide and 5 patients with both. Two patients did not receive any prior chemotherapy. All patients successfully achieved the target of 2.5 x 10⁶ CD34⁺ cells/kg in either one (15/19 patients) or two (4/19 patients) collections with the first apheresis product containing a mean of 5.79 x 10⁶ CD34⁺ cells/kg. Analysis of peripheral blood by flow cytometry demonstrated no significant differences in lymphocyte subsets before and after treatment with bortezomib. Following AHSCT, all patients successfully engrafted with a median time to neutrophil engraftment (ANC ≥ 500/mm³) of 11 days (range 9–14 days). Platelet engraftment (time to platelet count ≥ 20,000/mm³ sustained for 7 days without transfusion) occurred at a median of 12 days (range 9–30 days). Eleven patients were evaluable for response at 100 days post-transplant. Compared to pre-bortezomib paraprotein levels, 3 patients achieved a CR or near CR, 7 maintained a PR while 1 patient developed PD. We conclude that pretransplant treatment with 2 cycles of bortezomib does not adversely affect stem cell yield or time to engraftment in patients with MM undergoing AHSCT. Updated results and detailed analysis will be available at the time of presentation.