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. Here, CD33 is linked to acute myeloid leukemia.