In contrast, OXTR expression in cell lines and primary tumours was variable, with only two out of four ESR1+ breast cancer cell lines, one of three ERBB2 over-expressing cell lines, one basal origin tumour cell line, eight out of 17 (47%) estrogen nonresponsive cell lines, and 23 out of 56 (41%) primary tumours having detectable oxytocin receptor gene expression. Here, ESR1 is linked to breast cancer.