The low-frequency PRLR variants Ile76Val and Ile146Leu, which did not alter PRLR function or only altered PRLR function at supraphysiological prolactin concentrations (Fig. 4), respectively, likely represent PRLR benign polymorphisms, without clinical significance, and this is in agreement with recent reports from studies of women with breast cancer and fibroadenomas (43). Here, PRL is linked to breast cancer.