ABCG2 and neoplasm: The transportation of molecules into the TME, such as signaling lipids with established roles in tumor biology (for instance, prostaglandins, leukotrienes, and sphingosine-1-phosphate or SIP), and that are known to have profound effects on immune cells (for instance, microglia/macrophages), have been shown to be ABC transporter substrates (Cole, 2014; Fletcher et al., 2016).