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Treatment induced secondary malignancies after successful radiation and/or chemotherapy cure of primary tumors is a growing area of concern. The identification of chemopreventive compounds that reduce radiation-induced secondary malignancy but are both nontoxic and tolerated with long-term use is a critical need. We investigated the chemopreventive potential and mechanism of action of Vitamin E and EGCG (the active agent in green tea) with the human CGL1 radiation neoplastic transformation assay. The molecularly characterized CGL1 assay allows both alterations of the quantitative neoplastic transformation as well the potential underlying molecular processes of the chemoprevention to be determined. We found long-term treatment with 15 microM EGCG or 50 microM Vitamin E beginning 72 hours after 7 Gy irradiation, significantly reduce radiation-induced neoplastic transformation frequency by a factor of 2.3. We determined that Vit E suppressed radiation-induced carcinogenesis by the induction of a p53 and pro-apoptotic Bax dependent apoptosis in the progeny of the irradiated cells. In addition, we demonstrated that EGCG does not reduce radiation-induced carcinogenesis by increased apoptosis, but rather by the onset of p16 dependent senescence in the irradiated CGL1 progeny. Vit E and EGCG are excellent candidate nontoxic chemopreventive agents for radiation-induced carcinogenesis that work by two distinct molecular mechanisms. We propose that this information should also aid in the development of next generation chemopreventive compounds. These studies were supported by a grant from the DOD awarded to MSM. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4368.