Li et al. used a dual recombination system to perform lineage tracing of estrogen receptor (ER)-negative mammary luminal cells undergoing EMT in mouse mammary tumor virus polyoma middle tumor-antigen (MMTV-PyMT) transgenic mice and revealed that EMT was not activated in the tumor cells at the early stages, but was activated in the later stages of tumorigenesis, and that metastasis-initiating cells underwent EMT during metastasis [62]. Here, ESR1 is linked to neoplasm.