To clarify the clinicopathological importance of REG4 mRNA expression, we used GEO, TCGA, xiantao, UALCAN, and Kaplan-Meier plotter for a bioinformatics analysis in breast, cervical, endometrial and ovarian cancers. Compared to normal tissues, REG4 expression was found to be upregulated in breast, cervical, endometrial, and ovarian cancers (p < 0.05). Breast cancer had a higher level of REG4 methylation than normal tissues (