After verifying that we could detect PI3KCA E545K mutation from MCF7 cells alive or processed with the CellSearch®/DEPArrayTM workflow (70% and 80% detection rate, respectively, Figs. 2A and EV3A), we assessed CTCs obtained from a breast cancer patient (primary tumor: ER+, PR+, HER2 1+, Ki67 15%) with the UltraSEEK® Lung Panel, as this panel interrogates several genes of therapeutic interest like ERBB2, PIK3CA in breast cancer. This evidence concerns the gene PIK3CA and breast cancer.