GPER1 and breast carcinoma: Whereas some authors concluded that the activation of Src kinase, EGF-receptor, and the MAP-kinase Erk1/2 in breast cancer cells lacking ERα is elicited by GPR30 [11, 12], other authors predominantly hypothesize the presence of a truncated ERα that localizes at the membrane supported by the scaffolding protein caveolin [10].