APEX1 and cancer: The discrepancy with our prior work could be, we postulate, due to the following circumstances: a) the overall APE1 serum level was low and the sensitivity of the previous ELISA assay was too low to distinguish a difference between the levels in cancer patients from even lower levels in healthy donors; b) as APE1 level is altered by chemotherapeutic agents, only pretreatment or chemotherapy-naïve serum samples were analyzed in the current study, which should represent the cancer-associated level; or c) simply owing to the larger sample size in the present study.