ESR1 and breast cancer: (1)CART is expressed in primary and metastatic breast cancer.(2)CART stimulates cells by an autocrine and paracrine loop.(3)CART expression leads to the activation of MAPK pathway.(4)CART increases the ligand-independent activation of ERα through MAPK-mediated phosphorylation of ERα at S118.(5)CART is an independent poor prognostic factor in ER-positive lymph node negative tumors.(6)Ectopic CART expression in ER positive breast cancer cell lines promotes survival in tamoxifen treated cells.(7)High CART expression was associated with poor response to tamoxifen.