ABCG2 and cancer: Furthermore, since p75NTR is also present in Cancer Stem Cells (CSCs) and it is co-expressed with stemness markers, such as CD133 in LSCC [16], and with adenosine triphosphate (ATP)-binding cassette efflux transporter G2 (ABCG2) in tumors involving different organs, as well as in primitive hepatic and prostatic cancers [17], the possibility that p75NTR might be a novel CSC marker of LSCC has been also explored.