Just as allelic haplodeficiency of specific genes accounts for the del(5q) MDS phenotype, gene dosage of two dual specificity phosphatases encoded within or adjacent to the proximal CDR at 5q31, CDC25C, and PP2Acα, underlies the selective suppression of del(5q) clones by lenalidomide (31). This evidence concerns the gene CDC25C and myelodysplastic syndrome.