UCA1 and breast carcinoma: The lncRNA UCA1 has now been identified as a critical mediator of tamoxifen resistance in breast cancer by various mechanisms including sponging of miR-18a, a negative regulator of HIF1α [195], mTOR signalling [458], exosomal delivery of the lncRNA from resistant to sensitive cells [201], or via the Wnt/β-Catenin Pathway [190].