LIG4 and neuroblastoma: Notably, three genes overexpressed in differentiated cells and strongly down-regulated in the malignant stage (BIRC3, ERCC5, and LIG4) are key components of the DNA damage repair system, indicating that the malignant stage of NB cells is characterized by a constitutive genomic instability, which favoring the accumulation of novel mutations might, in turn, drive further stages of malignant transformation.