STS and endometriosis: In our study, we used primary human cells and a well-characterised model of in vitro decidualisation; however, it is conceivable that adaptive metabolism and alternative pathways may be more prominent in disease states such as endometriosis and endometrial cancer where increased expression of STS has been reported (Utsunomiya et al. 2004, Piccinato et al. 2016, Sinreih et al. 2017).