One size does NOT fit all – factoring weight into current stem cell transplant guidelines in multiple myeloma patients

Abstract Autologous hematopoietic stem cell (HPSC) transplantation serves as the standard of care treatment for multiple myeloma patients. The standard ASCT procedures for multiple myeloma (MM) patients often includes induction therapy, stem cell collection via apheresis and autologous hematopoietic cell transplantation (HCT) for eligible patients. The current guideline for HPSC collection for multiple myeloma established that 3x106 cells/kg of actual body weight (ABW) by the 1997 study of stem cell transplants in breast cancer. Recent research indicates that ideal body weight (IBW) utilization is a stronger predictor of post-autotransplantation neutrophil recovery than calculations based on ABW. Reducing the cost of HPSC collection and cryopreservation is critical to mitigate the cost incurred by the transplant center and the patient. This study evaluates whether using a patient’s IBW or Adjusted Ideal Body Weight (AIBW) would be satisfactory in determining the amount of stem cells required for transfusion when compared to ABW. After institutional review board approval, a retrospective chart review study analyzed a cohort of 224 deceased MM patients, who received HCT at the UAB Medicine Hospital within the fiscal years of 2017 to 2019. The ABW for each patient was used to calculate their IBW and AIBW using the formulas shown below. The target CD34+ cell amount for patients was calculated using each body weight parameter. The platelet count and absolute neutrophil count (ANC) defined a successful platelet and neutrophil engraftment. The engraftment date was determined as the day the platelet value exceeded 20 and ANC exceeded 0.5 for three consecutive days (without any transfusion within a seven day window) and a statistical analysis was utilized to determine whether the IBW and AIBW parameters were adequate to achieve successful engraftment and HCT. This study finds that the cohort of multiple myeloma patients are significantly more overweight than the prior study that established the current guidelines for autologous hematopoietic cell transplantation. The results for CD34+/kg cell targets for ideal and adjusted ideal body weight suggests that there are minimal differences in platelet and neutrophil engraftment and number of platelet transfusions when compared to CD34+/kg targets using actual body weight. Some methods to reduce excessive stem cell collection include decreasing target cell dosage from previous standards of 6.0 x 106 cells/kg or calculating total cell dosage with IBW or AIBW instead of ABW. Future studies should evaluate the efficacy of cell dosage decrease to lowered targets and total cell calculations using IBW or AIBW instead of ABW. Equation 1. ABW to IBW Conversion (H = height over 5 ft. in inches) IBW(males) = 50 kg + (2.3 kg x H) IBW(females) = 45.5 kg + (2.3 kg x H) Equation 2. ABW to AIBW Conversion AIBW = IBW + 0.5(ABW-IBW)