ARNT and breast cancer: This is the motif for the agonist-activated heterodimer AHR/ARNT (Aryl hydrocarbon receptor/Arnt (hypoxia inducible factor 1 beta)) which directly associates with the estrogen receptors ER-alpha and ER-beta in ER-positive breast cancer, although its function in HER2-positive breast cancers is not well characterised [30].