NOTCH proteins (NOTCH1, NOTCH2, NOTCH3 and NOTCH4) play crucial roles in embryonic development. Also, mounting evidence indicates that NOTCH contributes to the pathogenesis of hematopoietic and solid malignancies. Recent studies reported a high incidence of gain-of-function mutations of the NOTCH1 gene in T-cell acute lymphoblastic leukemias (ALL).