Using this approach, a number of gene signatures were deduced for breast cancer phenotypes, including an "intrinsic" set for clustering of breast cancers [6], an "Amsterdam" signature consisting of 70 genes [7], a 76-gene "Rotterdam" signature [8] for metastasis, and a set of 21 genes associated with disease outcomes for ER+ tumors [9]. This evidence concerns the gene ESR1 and breast cancer.