E2F1 and cancer: Our analysis for intron-APAs included genes with important functions in DDR and cancer (Figure 4c), namely cyclin-dependent kinase inhibitor 1A (CDKN1A, p21) [44, 45], polymerase (RNA) II (DNA directed) polypeptide A (POLR2A, RNA polymerase II) [46, 47], Ephrin B2 (EFNB2) [48, 49], E2F transcription factor 1 (E2F1) [50, 51] and Down syndrome critical region gene 3 (DSCR3) [52, 53].