APEX1 and nasopharyngeal carcinoma: Furthermore, the genomes of EBV-positive tumors contain a greater mutational load compared with the EBV-negative variants [31], and polymorphisms of the BER effectors OGG1, APE1, and XRCC1 are associated with increased risk of NPC in the Chinese population [32], suggesting that the oxidative stress associated with infection may play an important role in carcinogenesis.