EPX and breast cancer: However, it is unknown if additional 3’ nucleases are required to cooperate with nuclease-proficient Pol δ and Pol ε to maintain high-speed elongation, or to proofread DNA elongated by Pol α or other 3’->5’ exonuclease-deficient polymerases-like translesion DNA polymerases or mutant Pol δ and Pol ε identified in certain human cancers, including colorectal cancer, breast cancer, and glioblastoma14.