The increase in CDKN1A expression after treatment with retinoids was described in many human malignancies under in vivo and in vitro conditions: acute promyelocytic leukemia [52], acute T-lymphoblastic leukemia [53], pre-B lymphoma [54], hepatoblastoma [55,56], and neuroblastoma [57-60]. This evidence concerns the gene CDKN1A and neuroblastoma.