ABCG2 and breast carcinoma: Although in breast cancer the resistance signaling pathways induced by PX remains unclear, it is known that it can induce the activation of the nuclear factor kappa B (NF-κB) pathway [6], and this can in turn regulate the expression of genes related to multidrug resistance proteins (MRPs) like ABCG2, which actively transport PX to the extracellular space, inhibiting its action [7].