ESR1 and breast cancer: We confirmed that a broad range of breast cancer cell lines, including triple-negative breast cancer (TNBC) cell lines MDA-MB-231 and MDA-MB-436 cells, estrogen positive (ER+) MCF7 cells and HER2 positive (Her2+) BT474 cells, highly expressed Muc1 protein on their surface (Fig. 2A), suggesting that Muc1 is a good target, at least, for a broad range of breast cancers.