S100PBP [68], PRR4 [69], ANKEF1 [39,70], EPCAM [71], SPDEF [72], KRT8, KRT19 [73], KIAA1324 [74,75], CXCR4 [76,77], AGR2 [78,79,80], SCNN1A [81], AP1M2 [82], CLDN4 [83], and ERBB3 [84,85] have been reported to have correlations with breast cancer or have been identified as biomarkers for diagnosis, metastasis, and prognosis of breast cancer and even as therapeutic targets. Here, CLDN4 is linked to breast cancer.