ABCG2 and neoplasm: Gene expression alterations in the genes associated with stemness such as aldehyde dehydrogenase 1—ALDH1 isoforms (ALDH1A1, ALDH1A2, ALDH1A3, ALDH1B1), octamer-binding transcription factor 4 (OCT4), Nanog homeobox (NANOG), sex determining region Y-box 2 (SOX2), ATP binding cassette subfamily G member 2 (ABCG2), prominin-1 (CD133), endosialin—microvascular marker implicated in tumor angiogenesis, and multidrug resistance-associated protein 1 (MRP1) were assessed (Figure 2A).