PRISMA article flow diagram. Group 1 studies are those in which patients randomly assigned between maintenance and observation were similar with regard to previous treatments (preplanned, stratified randomization, or differences accounted for in multivariate analysis). “Alternative design” refers to studies in which either patients randomly assigned between maintenance and observation were dissimilar with regard to previous treatments (induction and/or consolidation) or none of the strategies mentioned in group 1 were used to account for potential differences between the groups. Also included in this group are studies in which patients received intensification courses (in addition to standard consolidation) that are not standard in today’s practice, as well as studies without an observation-only arm or those evaluating maintenance therapies after auto-HCT.