ABCG2 and cancer: As an exporter, ABC transporters can influence the inflammatory response by transporting paracrine hormones such as prostaglandins and leukotrienes or even interleukin-1β from cancer stem cells, culminating in activations of extracellular G-protein-coupled receptors or cytokine receptors, creating microenvironments that promote survival, angiogenesis, and migration [23].