GSTO1 and breast cancer: Also, exposure of breast cancer cells lines to chemotherapy leads to an enrichment of BCSCs by the induction of glutathione S-transferase omega 1 (GSTO1), the cystine transporter xCT and the regulatory subunit of glutamate-cysteine ligase (GCLM) dependent on hypoxia-inducible factor 1 (HIF-1) and HIF-2.