PROM1 and neoplasm: How tumor-initiating cells are defined or supported in this study is by various means, including correlation with CD133 which is a widely reported surrogate marker of liver cancer stem cells5,6,8, (ii) correlation with stemness/undifferentiated signatures defined by CytoTRACE27 and cancer stemness index30, etc. Most importantly, (iii) tumor-initiating ability (self-renewal) is functionally defined by in vitro and in vivo limiting dilution assays, experiments that are now widely accepted in the field43.