Patients with multiple myeloma (MM) who undergo high dose therapy (HDT) followed by autologous stem cell transplantation (ASCT) and achieve a complete response (CR) have a superior overall survival (OS) and time to progression (TTP). Thus achieving a CR is an important goal of therapy with ASCT. Cyclophosphamide has significant activity against MM and is often used in high doses prior to ASCT for mobilization of hematopoietic stem cells. We hypothesized that high dose cyclophosphamide (HDC) may further improve CR rates in patients undergoing ASCT.

Methods: The Mayo Clinic myeloma transplant database was searched for patients without circulating myeloma cells who had stem cell mobilization with hematopoietic growth factor (HGF) alone or HDC followed by HGF. Relevant demographic, clinical and laboratory characteristics were abstracted. The main outcome studied was the impact of HDC on CR rates and time to progression (TTP) to myeloma.

Results: We identified 201 patients without circulating myeloma cells. Of these, 127 were mobilized with HDC and HGF and 74 with HGF alone. The two cohorts were similar with respect to age, gender, isotype, B2M, plasma cell labeling index, cytogenetics, conditioning regimen, disease status at time of transplant with no statistically significant differences between the two cohorts. CR rates were 37.4 and 41.3% (p=0.6115) for patients mobilized with HDC/HGF and HGF respectively. TTP was 19.9 and 17.6 months (p=0.6039) respectively. The median number of collection sessions for patients mobilized with HDC/HGF was 2 (1–10) and those mobilized with HGF was 4 (1–10) (p<0.0001). In a multivariate analysis for TTP, cytogenetics and achieving a CR were the only independent variables (p=0.0012 and p<0.0001).

Conclusion: HDC for autologous hematopoietic stem cell collection reduces the number of collections necessary to support HDT/ASCT. However, HDC does not increase CR rates or improve on TTP for patients undergoing ASCT.