NOX4 and neoplasm: Recent studies have demonstrated that NADPH oxidase subunit 4 (Nox4) is expressed in several tumor types such as hepatoma [12], breast cancer [13], ovarian cancer [14], melanoma [15], prostate cancer [16], and various neuroepithelial neoplasms [17], and is involved in cellular senescence, resistance to apoptosis, tumorigenic transformation, cell proliferation, cell survival, and radiation resistance.