Tocotrienols have been shown to have a high affinity for ERβ, but not for ERα, and to exert antiproliferative and pro-apoptotic effects through the nuclear translocation of ERβ and the expression of pro-apoptotic estrogen-responsive genes in ERβ-expressing breast cancer MDA-MB-231 cells and in human breast cancer MCF-7 cells expressing both ERα and ERβ [37,38]. This evidence concerns the gene ESR1 and breast cancer.