PECAM1 and chronic myelogenous leukemia, BCR-ABL1 positive: Previous studies[19,21] from our laboratory have identified Flk1+ (fetal liver kinase-1 positive) CD31-CD34- cells carrying the BCR/ABL fusion gene from the bone marrow of Philadelphia chromosome positive (Ph+) patients with CML and found that these cells could differentiate into malignant blood cells and phenotypically defined endothelial cells at the single-cell level, suggesting these cells have the properties of hemangioblasts.