ESR1 and breast cancer: Higher expression has been found in ER-negative types (p = 0.019 [52]; p < 0.002 [55]; p < 0.05 [63]), TNBC (p < 0.0001 [47]; p < 0.01 [48,49]) and HER2+ (p = 0.0009 [47]; p < 0.05 [48,49]; p < 0.0001 [50]) than in ER+ types of breast cancer.