Analysis of immunohistochemistry for epithelial markers (CK5, CK8, CK14, CK18, E-cadherin, and epithelial specific antigen) and for clinical biomarkers (ER, PR, Her2, Ki67, and p53) showed these features were similar in matched pairs of PDTX model and originating breast cancer sample and were consistently retained with passaging (Figure S2A and Table S2 for summary of the data). Here, ERBB2 is linked to breast cancer.