Furthermore, to confirm and understand the role of PKD1 in breast cancer, we analysed the expression pattern of PKD1 mRNA in a series of 38 non-cancerous or malignant breast cell lines and 152 ERα-positive breast tumours from tamoxifen-treated patients with long-term follow-up and its association with tamoxifen responsiveness and classical clinicopathological prognostic factors. Here, ESR1 is linked to breast cancer.