ESR1 and breast cancer: To determine whether eIF4E might play a role in mediating tamoxifen resistance via the estrogen-dependent pathway, constitutive expression of eIF4E, ERα and FOXM1 were correlated in a panel of breast cancer cell lines; tamoxifen sensitive MCF-7 and ZR-75, and tamoxifen-resistant LCC2 (ER+) and AK-47 (ER−) cells, together with non-neoplastic breast epithelial cell MCF-10A which expresses low levels of all three genes.