Cyclophosphamide Overcomes the Suppressive Effect of LenalidomideTherapy on Stem Cell Collection in Preparation for Autologous Stem Cell Transplantation for Multiple Myeloma.
Authors: Mark Tomer , Jayabalan David , Pearse Roger N. , Stern Jessica , Furst Jessica , Rambo April , Harpel John , Shore Tsiporah , Schuster Michael , Leonard John P. , Christos Paul J. , Coleman Morton , Niesvizky Ruben 
Published: October 2019

Abstract
Multiple Myeloma (MM) therapy has evolved over recent years to include powerful new therapeutic agents. The goal for most patients with MM, however, still remains high-dose chemotherapy followed by autologous stem cell transplantations as this procedure has been proven to have a therapeutic benefit. Therefore, the selection of an induction therapy must take into consideration the potential impact on the ability to collect enough stem cells for future transplantation. Recent studies have discussed difficulty in collecting stem cells in patients receiving lenalidomide-based induction therapy using filgastrim (G-CSF) in preparation for autologous stem cell transplantation in MM. It also has been recommended that the duration of lenalidomide induction therapy be limited to 4–6 cycles, since longer treatment time can hinder collection yields. We sought to determine if the addition of cyclophosphamide (CTX) to G-CSF as a mobilization regimen could rescue the ability to collect adequate stem cells for at least two autologous stem cell transplants for patients who had induction therapy with the BiRD (Biaxin® [clarithromycin]/Revlimid® [lenalidomide]/dexamethasone) regimen. BiRD therapy is as follows for each 28-day cycle: Clarithromycin 500mg po BID for days 1–28, Lenalidomide 25mg po daily for days 1–21, and Dexamethasone 40mg po weekly on days 1, 8, 15, and 21. All patients had either Stage II or III MM by Salmon-Durie criteria and were treatment naïve. Patients were advised to undergo stem cell collection after either maximum disease response or disease plateau had been achieved. Prior to stem cell mobilization, BiRD therapy was held for a minimum of 14 days. Stem cell collection was performed after either G-CSF alone at a dose 10 mcg/kg/day for 5–10 consecutive days until a total of 10 × 106/kg CD34+ stem cells had been collected or with the addition of cyclophosphamide (CTX) at a dose of 3g/m2 once prior to the initiation of G-CSF therapy. A total of 28 patients underwent stem cell collection. Stem cell mobilization was attempted with G-CSF alone in 9 instances and with CTX+G-CSF in 20 instances (1 patient underwent mobilization with both G-CSF alone and CTX+G-CSF). In comparison to the G-CSF monotherapy, CTX+G-CSF yielded a significantly greater stem cell collection (mean CD34+ cells collected: 3.78 × 106/kg vs. 32.33 × 106/kg, P < 0.0001). Only 33% of patients who attempted stem cell mobilization with G-CSF alone obtained sufficient CD34+ cell yield vs. 100% of the patients mobilized with CTX+G-CSF (P < 0.0001). The extent of BiRD therapy prior to stem cell mobilization ranged from 2–27 cycles. The number of cycles of BiRD did not significantly impact the success rate of stem cell collection (P = 0.14). In conclusion, the patients mobilized with CTX+G-CSF had a higher number of CD34+ cells collected and were all able collect enough stem cells for two autologous transplants. There was no association with the duration of BiRD therapy and successful CD34+ cell collection. We therefore recommend continuing lenalidomide-based induction therapy until desired tumor reduction goal is achieved and using the CTX in addition to G-CSF to ensure successful stem cell harvest prior to autologous transplantation.