ALDH1A1 and neoplasm: Hypoxia-induced enrichment of ALDH1+ cells and mammosphere-forming cells was impaired in MDA-MB-231 and MCF-7 subclones with NARF knockdown.62 When MDA-MB-231 subclones were injected into the mammary fat pad of immunodeficient mice (2 × 106 cells, such that BCSCs were not limiting for tumor initiation), there was no difference in primary tumor growth rate between cells expressing a non-targeting control shRNA (NTC) and cells expressing either of 2 different shRNAs targeting NARF, but lung metastasis of NARF-knockdown cells was markedly impaired.