PRICKLE1 and breast cancer: However, TNBC is highly invasive with strong metastatic propensity.1 We recently identified PRICKLE1 as a poor-prognosis marker in breast cancer.2 PRICKLE1 is a member of a conserved group of proteins involved in planar cell polarity (PCP) pathway.3 This pathway is well characterised in epithelial tissue morphogenesis during embryonic development of invertebrates and vertebrates.