ESR1 and breast carcinoma: The expression of PRLr has been studied in normal, benign, and malignant breast tissue, and one immunohistochemical study that evaluated paraffin wax-embedded sections of 102 breast biopsies revealed that the receptor was expressed in more than two-thirds of female breast carcinomas and that positivity was correlated with moderate and strong staining for the ER in tissue sections [23].