CD44 and cancer: Epithelial splicing regulatory protein 1 (ESRP1) is an epithelial cell-specific splicing factor, whose downregulation is associated with epithelial–mesenchymal transition (EMT) by regulating alternative splicing of multiple genes, such as CD44, CTNND1, ENAH, and FGFR2. Consistent with the downregulation of ESRP1 during EMT, it has been initially revealed that high ESRP1 expression is associated with favorable prognosis and ESRP1 plays a tumor-suppressive role in cancer progression.