Attrition and withdrawal in multiple myeloma randomized controlled trials: A systematic review

Patients with multiple myeloma (MM) enrolled in randomized control trials (RCTs) discontinue treatment for various reasons; however, no prior study has analyzed reasons for discontinuation. We performed a systematic review of MM RCTs to investigate reasons for treatment discontinuation, imbalances between trial cohorts, and reporting practices.A comprehensive search for RCTs in MM from 2015 to 2021 identified 45 studies meeting inclusion criteria.Of 21 236 randomized patients, 10 161 (47.8%) discontinued therapy by primary endpoint ascertainment. Causes of discontinuation included progression (n = 4790; 22.6% of randomized patients); toxicity (n = 2569; 12.1%); patient/physician withdrawal (n = 1200; 5.7%) and death (n = 495; 2.3%). Of randomized patients, 20 914 (98.5%) were included in the RCT analysis. Imbalances of attrition, defined as trials with greater than 5% absolute difference in discontinuation rate for reasons other than death, progression, and toxicity between intervention and control arms, were found in 11 (24.4%) studies.Although progression is the most common reason for RCT treatment discontinuation in patients with MM, over 10% discontinued due to toxicity. Furthermore, 24.4% of trials showed substantial imbalances between trial cohorts; raising concern for informative censoring and emphasizes the importance of detailed characterization of withdrawal in MM RCTs.