While some studies have shown an increased expression of LEF1 in both premalignant thymocytes and T-ALL [16], others have reported the deletion of the LEF1 gene accompanied with NOTCH1 and PTEN mutations, biallelic INK4A/ARF (CDKN2A) deletions, or activating PI3K or AKT gene mutations in T-ALL [16,21,22]. This evidence concerns the gene CDKN2A and acute lymphoblastic leukemia.