ESR1 and breast cancer: Taken together, BMI was the only breast cancer risk factor influencing cell proliferation at different levels: BMI did not only influence estrogen levels (Pemp et al. 2020) which in turn influenced activation of ESR1 but also intracellular signaling by influencing levels of TGFB1 which—in line with the molecular role of TGFB1 in intracellular signaling of non-cancer cells—in turn influenced markers for senescent cells positively.