Bortezomib Added to the Standard Mobilization Regimen of G-CSF and High-Dose Cyclophosphamide Is a Safe and Effective Combination for a High Yield Stem Cell Collection While Promoting Further Tumor Mass Reduction in Myeloma.

Standard stem cell mobilization regimens for multiple myeloma patients include G-CSF alone or in combination with high dose cyclophosphamide. Given the known in vitro and in vivo synergy between alkylating agents and proteosome inhibitors, we sought to optimize the potential for concurrent cytoreduction by adding bortezomib to the mobilization regimen. Five evaluable patients, whose prior therapy consisted of six cycles of a 21-day treatment with bortezomib/dexamethasone +/− pegylated liposomal doxorubicin, were mobilized. They received IV push bortezomib at 1.3 mg/m² on days 1, 4, 8, and 11 in combination with high-dose cyclophosphamide at 3mg/m² and MESNA on day 8. G-CSF was given for 10 consecutive days starting on day 9. One patient began this regimen in nCR, two were in PR, and two were in CR by urine and serum immunofixation and bone marrow evaluation. Stem cells were easily harvested from each of the five patients. The number of CD34+ cells collected far exceeded the amount normally mobilized with cyclophosphamide and/or G-CSF alone, with four out of 5 patients collected in a single day.

The two patients who began the mobilization cycle in PR continued to respond positively. Their protein levels dropped an additional 8.9 and 14.6 percent respectively during the last cycle. The patient who began mobilization in nCR achieved a CR by the end of treatment. Some expected toxicities associated with high dose cyclophosphamide and G-CSF occurred. All patients experienced grade 3 and 4 cytopenias, however, they recovered and were able to continue on to transplant. Serious adverse events of grade 3 chest pain (non-cardiac), grade 4 pneumonia, and grade 4 febrile neutropenia also occurred. Bortezomib in addition to high dose cyclophosphamide followed by G-CSF is a novel, well-tolerated and efficacious combination for stem cell mobilization in patients with multiple myeloma. This regimen not only yields a high number of stem cells within a short collection time, but may further cytoreduce disease as well.