A previous study by Liu et al. (Liu et al. 2018) showed immunohistochemical staining of the hypoxia marker HIF-1α in normal, eutopic, and ectopic endometria from women with endometriosis, where the transcription-active HIF-1α was indeed predominantly located in the nuclei of epithelial and stromal cells. Here, HIF1A is linked to endometriosis.