ROBO4 and acute myeloid leukemia: In AML, CD34 expression has been associated with poor clinical outcome [22, 23, 24], and CD38‐negative CD34‐positive leukemic cells demonstrate increased leukemia‐initiating capacity and show stem‐like features, a quiescent phenotype and increased expression of adhesion‐related molecules such as CD44, CXCR4, and integrins, as well as of the growth guidance receptor ROBO4 [25, 26].