Interestingly, the different pro-apoptotic gene expression patterns in response to vorinostat amongst AML PB-CD33 and MDS BM-CD33 cells and leukemic K562, HL60 and THP1 cells (Figs 4, 5, 6) suggests vorinostat promoted apoptosis of these cells via different molecular mechanisms. This evidence concerns the gene CD33 and myelodysplastic syndrome.