ESR1 and breast cancer: Based on the collected serum of postmenopausal breast cancer patients, it was found that circulating factors in the serum of postmenopausal obese women can enhance the cross-talk between the IGF-IR, PI3K/AKT and MAPK signaling pathways with nongenomic ERα signaling, which stimulates the survival and growth of Erα-positive breast cancer cells, increases the resistance to aromatase inhibitor therapy and impacts the therapeutic effect (39).