ESR1 and endometrial cancer: A recent paper reported that women with variants of the aromatase (CYP19A1) gene that are associated with a 10-20% increase in circulating oestrogen levels after menopause have an increased risk of endometrial cancer [42], In the present study we have examined the patterns of expression of ERα, the full length ERβ receptor (ERβ1) and two ERβ splice variant isoforms (ERβ2, ERβ5) in well-characterised stage I endometrioid adenocarcinomas.