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). This evidence concerns the gene ESR1 and breast cancer.