BMP4 and acute lymphoblastic leukemia: The role of the BMP signalling pathway in leukaemia progression is beginning to be revealed [23,24], and particularly for ALL, the increased production of BMP4 by bone marrow mesenchymal stem cells at diagnosis and the up-regulated expression of some BMP ligands by ALL blasts support a role for BMP signalling in this haematological disorder [25,26,27].