Another piece of evidence that supports the important role of hypoxia in IHs comes from the detoxifying enzyme aldehyde dehydrogenase 1 (ALDH1) that has been commonly used as a marker of stemness in breast cancer cells (BCSC), and under hypoxic conditions produces a phenotypical shift of BCSCs into a more proliferative subtype46. Here, ALDH1A1 is linked to breast cancer.