Chemopreventive Activity of Vitamin E in Breast Cancer: A Focus on γ- and δ-Tocopherol

Vitamin E consists of eight different variants: alpha-, beta-,.gamma-, and delta-tocopherols (saturated phytyl tail) and alpha-, beta-,gamma-, and delta-tocotrienols (unsaturated phytyl tail). Cancer prevention studies with vitamin E have primarily utilized the variant alpha-tocopherol. To no avail, a majority of these studies focused on variant alpha-tocopherol with inconsistent results. However, gamma-tocopherol, and more recently delta-tocopherol, have shown greater ability to reduce inflammation, cell proliferation, and tumor burden. Recent results have shown that gamma-enriched mixed tocopherols inhibit the development of mammary hyperplasia and tumorigenesis in animal models. In this review, we discuss the possible differences between the variant forms, molecular targets, and cancer-preventive effects of tocopherols. We recommend that gamma-enriched mixture, gamma- and delta-tocopherol, but not alpha-tocopherol, are promising agents for breast cancer prevention and warrant further investigation.