Drugs that specifically target the inverted methylation pattern of cancerous cells include the DNA methyltransferase inhibitors azacitidine[120][121] and decitabine.[122][123] These hypomethylating agents are used to treat myelodysplastic syndrome,[124] a blood cancer produced by abnormal bone marrow stem cells.[11] These agents inhibit all three types of active DNA methyltransferases, and had been thought to be highly toxic, but proved to be effective when used in low dosage, reducing progression of myelodysplastic syndrome to leukemia.[125]