ESR1 and breast cancer: Recently, Speyer et al.[31] have demonstrated that activation of GRM1 with L-quisqualate results in phosphorylation of AKT in estrogen receptor negative (ER-) breast cancer cells, that this phosphorylation can be abrogated through pre-treatment with a GRM1 inhibitor, and that GRM1 inhibition results in reduced cell growth in vitro and in vivo.