ESR1 and breast cancer: Specifically, we performed MSC on single-cell transcriptome atlas of breast cancer by Wu et al. 2021[35], encompassing 26 breast cancer primary tumors of diverse subtypes by hormonal status (estrogen receptor (ER), progesterone receptor (PR) status), Her2 signaling status (Her2 amplification/deletion) and by molecular PAM50 subtyping[35].