A new metric, termed Tumor MicroEnvironment of Metastasis (TMEM) [4], also known as MetaSite Score [5], has recently been shown to be prognostic of metastatic risk in estrogen receptor positive / human epidermal growth factor receptor 2 negative (ER+/HER2−) breast cancer, independent of the four-stain immunohistochemical assay (IHC4) [6], the genomic clinical recurrence biomarker (OncotypeDx score) [2], and classical clinicopathologic features [7] and was clinically validated [5,7]. Here, ESR1 is linked to breast cancer.