ESR1 and breast cancer: In a study performed by De Santi et al., the breast cancer cell lines MCF-7 (ER positive) and MDA-MB-231 (triple-negative) have been analyzed in response to CTet treatment in terms of cell cycle perturbations and autophagy induction [170], and the ER stress response was considered as the main upstream CTet molecular mechanism for both MCF-7 and MDA-MB-231 cells [196].