Deletion of a single IKZF1 allele or mutations of a single copy of IKZF1 were firstly detected in 15 % of all cases of pediatric B-cell ALL and in more than 80 % of Ph+lymphoid leukemia cases, either de novo Ph+ ALL or chronic myeloid leukemia at progression to lymphoid blast crisis [15, 22, 23]. This evidence concerns the gene IKZF1 and lymphoid leukemia.