Among the histological subtypes, solid carcinoma (p = 0.004), anaplastic carcinoma (p = 0.009), ductal carcinoma (p = 0.018) and carcinoma arising in a benign tumor (p = 0.049) exhibited significantly lower PRLR expression levels than non-neoplastic mammary tissue of fresh frozen samples (Fig 3). Here, PRLR is linked to undifferentiated carcinoma.