The emergence in recent years of the first mammalian haploid cell lines has raised great expectations in the scientific community. Despite their potential, these cultures present some issues that complicate their use because haploidy is unstable and can be lost quickly. The Genomic Instability Group at the Spanish National Cancer Research Centre (CNIO) has offered an explanation of this phenomenon and proposes a way to overcome it. This work has been published in the journal Proceedings of the National Academy of Sciences (PNAS).