PDX1 was derived from untreated HER2+ breast cancer, carrying E365K mutation in C2 PI3K-type domain of PIK3CA gene, while PDX2, with PIK3CA H1047R hotspot mutation in kinase domain, was derived from a tumor pretreated with several rounds of trastuzumab with vinorelbine, another tubulin-binding chemotherapeutic drug (see Methods for details). This evidence concerns the gene ERBB2 and breast cancer.