POU5F1 and lung cancer: To identify CSCs in lung cancer, specific biomarkers have been characterized, including ATP binding cassette subfamily G member 2 (ABCG2), aldehyde dehydrogenase (ALDH), CD166/Nanog homeobox (NANOG), CD133/prominin 1 (PROM1), CD44, CD117/KIT, and POU class 5 homeobox 1 (POU5F1, formerly known as OCT3/4) [359, 360].