High-Dose Cyclophosphamide: An Effective Non-Transplant Salvage Option in Relapsed/Refractory Multiple Myeloma.
Authors: Ailawadhi Sikander , Keng Michael , Thara Eddie , Hendifar Andrew , Price Tanya , Hanna Lisa , Mark Lisa , Mohrbacher Ann 
Published: October 2019

Abstract
Abstract 4947

Background
Recent advances in the treatment of multiple myeloma (MM) have significantly improved overall survival. With MM patients living longer, there is a constant need to find better therapeutic options, especially when patients are refractory to conventional agents, and are not eligible for experimental therapeutics in clinical trials. We evaluated treatment with single-agent high-dose cyclophosphamide (HDCy) in a cohort of heavily pre-treated patients with relapsed/refractory MM.

Methods
All the patients were previously treated for active MM at the University of Southern California (USC), Los Angeles, CA. Cyclophosphamide was administered at 1.2 gm/m2 in D5W intravenous (IV) over 1 hour every 3 hours for a total of 4 doses. Mesna was given to prevent urinary adverse events from cyclophosphamide as 4 gm/m2 in 1000 ml D5W IV to run at 50 ml/hr for 20 hours, starting 15 minutes prior to the first dose of cyclophosphamide. Patients were given pre-medications with 5HT3 antagonists an steroids. Treatment was administered in the in-patient setting and patients were discharged after the last dose of cyclophosphamide. Treatment was repeated every 4 weeks, if well-tolerated and continued response. Growth factor support was provided to the patients, as needed. Response to treatment was assessed after each 4-week cycle according to the International Uniform Response Criteria for MM.

Results
Seven patients (4 females, 3 males) were treated on this regimen with a median age of 53 years (range 34-61 yrs). These patients included 3 Hispanics (43%), 2 Asians (29%), 1 Caucasian (14%) and 1 African-American (14%). MM subtype was IgG disease in 3, IgA in 2, and light-chain only in 2 patients. Advanced stage disease (>stage 1) at the time of diagnosis as per the Durie Salmon (DS) staging system was present in 71% of the patients, while 3 patients (43%) had advanced stage disease as per the International Staging System (ISS). Four patients (57%) had lytic bone disease at the time of diagnosis, while only 1 patient was a non-secretor. Five of these patients (71%) never received an autologous stem cell transplant (ASCT) as a part of their MM treatment. Median number of therapies in these patients was 5 (range 4-8), while median number of therapies prior to high-dose cyclophosphamide (HDCy) were 3 (range 2-7). Median number of cycles of HDCy administered to the patients was 2 (range 1-5). Overall Response Rate (ORR = CR+PR) was 29% (n=2) with 1 patient achieving CR and 1 patient achieving VGPR. Four patients (57%) had stable disease (SD) and 1 patient had progressive disease (PD). Thus, the overall clinical benefit (CR+PR+SD) was seen in 6 out of the 7 patients (86%). Median time to best response was 5 weeks (range 4-10 weeks). Median time to progression was 16 weeks (range 8-24 weeks). Most common adverse events were cytopenias and fatigue, but were easily manageable with supportive care on an out-patient basis.

Conclusions
Despite improvement in therapeutic regimens for MM, it remains an incurable disorder. There is a constant need to develop regimens for treatment of relapsed/refractory MM patients that are efficacious and well-tolerated. We report the use of single-agent HDCy in heavily pre-treated MM patients. Despite the small number of patients studied, we have noted meaningful clinical benefit with a manageable toxicity profile. This warrants further investigation into developing therapeutic regimens with high-dose cyclophosphamide.

Disclosures
No relevant conflicts of interest to declare.