ALDH1A1 and neoplasm: Consequently, SOX2 was silenced in mammospheres, formed from human tumor tissues (Fig. 5A) which resulted in down regulation of OCT4, NANOG, ALDH1A1, and most importantly, ABCG2 expression (Fig. 5B; p < 0.01), confirming a direct correlation of SOX2 with ABCG2.