EPAS1 and cancer: This, and the total infertility phenotype that ensues in global Epas1 knockout mouse lines23, underscores the importance of controlled oxygen tension in developing in vitro growth (IVG) and IVM technologies for clinical practice, particularly for women and girls who are seeking to safeguard their future fertility in response to a cancer diagnosis46 or for those at risk of ovarian hyperstimulation syndrome47.