4-tert-Octylphenol stimulates the expression of cathepsins in human breast cancer cells and xenografted breast tumors of a mouse model via an estrogen receptor-mediated signaling pathway

► Cathepsins B and D were markedly enhanced by octylphenol (OP) in MCF-7 cells. ► OP may accelerate breast cancer cell growth and cathepsins via ER-mediated signaling. ► Breast cancer cells exposed with OP to mouse model were more aggressive. ► OP can promote metastasis through the amplification of cathepsins B and D via ER-mediated signaling pathway.