In the 1990s, studies showed tocotrienols are the components of vitamin E responsible for growth inhibition in human breast cancer cells in vitro, through estrogen-independent mechanisms. Tocotrienols work synergistically with tamoxifen, a commonly used breast cancer medicine, in killing cancer cells.
Tocotrienols can also affect cell homeostasis, possibly independently of their antioxidant activity. Anti-cancer effects of α- and γ-tocotrienol have been reported, although δ-tocotrienol was verified to be the most effective tocotrienol in inducing apoptosis (cell death) in estrogen-responsive and estrogen-nonresponsive human breast cancer cells. Based on these results on cells in culture, investigators have hypothesised that a mixture of α- and γ-tocotrienols might reduce breast cancer risk.
Further studies on tocotrienol and breast cancer indicated that gamma-tocotrienol targets cancer cells by inhibiting Id1, a key cancer-promoting protein. Gamma-tocotrienol was shown to trigger cell apoptosis as well as anti-proliferation of cancer cells. This mechanism for δ- and γ-tocotrienol was also observed in separate prostate cancer and melanoma cell line studies.
In 2009, a study by scientists at the College of Pharmacy, University of Louisiana at Monroe, showed that lower level statin treatment in combination with γ-tocotrienol inhibits growth of highly malignant +SA mammary epithelial cells in culture (suggesting the possibility of avoiding myotoxicity associated with high dose statin monotherapy).