CD34 and myelodysplastic syndrome: Moreover, up-regulation of Hh pathway components has been observed in the tumor stem cells of numerous hematologic malignancies, including BCR-ABL+ leukemic stem cells (LSCs)[65,68], clonogenic B-ALL cells[87], CD34+ acute myeloid leukemia (AML)– and myelodysplastic syndromes (MDS)–derived cells[77], and MM CD138− tumor stem cells[91].