Bortezomib washout duration prior to stem cell mobilization in patients with newly diagnosed multiple myeloma

Objectives We aimed to determine the impact of washout period in patients with multiple myeloma between bortezomib‐based induction regimens and the collection of stem cells. Methods This was a single‐center historical prospective study, including all sequential newly diagnosed patients with myeloma between 2012 and 2017 that were given a first‐line bortezomib‐based induction therapy (≤6 cycles) followed by stem cell collection (n = 75). Results We found a statistically significant correlation between the days from last dose of bortezomib and both CD34 + cells/kg yield on the first collection day and the overall collected CD34 + cells/kg ( r  = .466, P  < .001, and r  = .341, P  = .03, respectively). The optimal receiver operating curve's cutoff point was 8.5 days (79% sensitivity and 71% specificity, P  = .001). On multivariate analysis, timing of last dose of bortezomib remained statistically significant ( P  = .01). Based on this, we developed a model to predict the total collected CD34 + cells/kg = 11.76 + 0.13 (timing in days of last dose of bortezomib) −0.1 (age) −1.39 (if female) −0.01 (≥PR) −1.35 (if prior radiation). Conclusions Timing of last dose of bortezomib may predict a successful collection. A washout period of 9 days is associated with a better collection yield. A prospective validation of this novel finding is required.