ESR1 and breast carcinoma: First, to observe the dynamic changes in BCs during breast cancer progression, we selected all 11 clusters of BCs (Figure 2B) and analyzed the ER scores of the putative BCs using the R software package genefu.[19] Consistent with the immunohistochemical results in Figure 1E, BCs from W6 and W8 MMTV‐PyMT mice showed higher ERα expression than those from W10 and W12 MMTV‐PyMT mice (Figure 2C).