Messenger RNAs encoding variant forms of both ERα (Bollig and Miksicek, 2000) and ERβ (Lu et al, 1998) have been identified in breast cancers and in breast cancer cell lines and there has been considerable debate over the role of such variants in cancer progression (Balleine et al, 1999; Huang et al, 1999). Here, ESR2 is linked to cancer.