PRDX4 and oral cavity squamous cell carcinoma: Increased expression of PRDX4 has been observed in many cancers, including prostate cancer [5], glioblastoma [6], oral cavity squamous cell carcinoma [7], and ovarian cancer [8], whereas decreased expression of PRDX4 in tumors was only reported in very few cancers, for example, in acute promyelocytic leukemia [9] and gastric adenocarcinoma [10].