CYP26A1 was upregulated >5-fold in cases compared with controls and is of particular interest since it is a progesterone-regulated gene 58,59 that has been found also to be upregulated in the proliferative phase for rAFS stage III/IV cases vs. stage I/II 19, while it was found to be nominally downregulated in endometriosis cases vs. controls in the secretory phase.22 This evidence concerns the gene CYP26A1 and endometriosis.