ESR1 and metastatic neoplasm: The insignificant difference of ESR1 amplification between invasive and non-invasive breast cancers suggests that ESR1 copy number alteration might not be used as a key predictive marker for invasion and metastasis, however its enrichment in recurrent disease, especially after endocrine therapy treatment, suggests that it likely plays a role in intrinsic and/or acquired resistance to endocrine therapy and metastatic disease progression[45–48].