GPX4 and cancer: We noted that the CD44low/−/ALDH1high microniches with A-to-I-edited GPX4 variants had high ferroptosis-associated gene set level changes with high expression levels of GPX4. With recent findings that breast tumours maintain a reservoir of subclonal diversity43, we sought to investigate whether the GPX4 A-to-I editing event is related to residual cancer microniches.