ESR2 and breast carcinoma: The situation is complicated further by the identification of a number of splice variant isoforms of the human ERβ gene (Moore et al, 1998), the mRNAs for which have been detected in breast cancer tissues and breast cancer cell lines (Fuqua et al, 1999; Speirs et al, 2000; Poola et al, 2002a, 2002b).