Ishimaru S, Okamoto Y, Imai C, et al. - In this investigation, researchers explained the clinical features and results of 12 Japanese pediatric hypodiploid ALL patients, including those who had hematopoietic 13 stem cell transplantation. From the registries of prospective multicenter trials conducted by the four independent clinical study groups in Japan between 1997 and 2012, clinical data of hypodiploid ALL cases were retrospectively collected. In total, 117 ALL patients with hypodiploidy were analyzed. The results of Japanese ALL patients with less than 44 chromosomes were poor, as previous trials in other countries have reported. Although the sample size was small, there were better prognoses in patients with 44 chromosomes than those reported previously. In order to improve outcomes for pediatric ALL patients with less than 44 chromosomes, additional studies including international collaboration are required.