Activating mutations of cytosolic 5′-nucleotidase II (NT5C2) occurred in 6/18 type-1 and 8/20 type-2 relapses and in none of the initial diagnosis samples, thus confirming the frequent acquisition of NT5C2 mutations in T-ALL relapses [8–10]. This evidence concerns the gene NT5C2 and acute lymphoblastic leukemia.