The ‘Reverse Warburg’ could be induced in CAFs by breast cancer cells through the abnormal activation of an estrogen/GPER/cAMP/PKA/CREB signaling axis; glycolytic CAFs, in turn, fed tumor cells with extra pyruvate and lactate, increasing mitochondrial activity and conferring breast cancer cells with drug resistance to several conventional clinical treatments, including endocrine therapy, HER2 targeting and chemotherapy [93]. Here, GPER1 is linked to breast carcinoma.