ESR1 and invasive ductal breast carcinoma: The lesion in the left lower inner region of the left breast was an invasive ductal carcinoma of the breast [enhanced type, pT1b, pN0, cM0, Stage IA, estrogen receptor (ER)-positive (95%), progesterone receptor (PR)-positive (< 1%), HER2 score 2 equivocal, HER2- FISH-positive, Ki-67 labeling index 18%] (Fig. 5a).