(6) When cell polarity and cell contact are lost in epithelial cells, specific epithelial markers (such as E-cadherin and cytokeratin) are reduced, and mesenchymal characteristics (such as increased cell motility, vimentin, N-cadherin, fibronectin, and matrix metalloproteinase) increase, activating ABC transporters and regulating anti-apoptotic pathways, thus participating in tumor resistance to cytotoxic drugs, tyrosine kinase inhibitors, and endocrine therapy [11]. Here, ABCG2 is linked to neoplasm.