When comparing the mutational landscape of CTC samples to the matched, synchronous bulk tumor, we observed that 38% (TNBC patient #1), 55% (HER2+ patient #2), 22% (ER+ patient #3) of all bulk SNVs were found at least once in the CTC samples (Fig. 1a–c, Supplementary Tables 3–5). This evidence concerns the gene ESR1 and neoplasm.