FEN1, a structure-specific endonuclease with multiple functions, plays an important role in DNA replication and repair.13 It is involved in a variety of biological functions, including Okazaki fragment maturation, base excision repair (BER), and trinucleotide repeats.22 Thus, FEN1 is a central component in DNA replication and repair,11,13 and its defects can lead to genomic instability and cancer susceptibility. Here, FEN1 is linked to cancer.