While some authors report that human tumor growth is associated with decreased plasma levels of cysteine and homocysteine [69], more recently other authors demonstrated that antioxidants such as N-acetylcysteine (a direct precursor of cysteine) can accelerate tumor progression by decreasing ROS levels, DNA damage and p53 (a tumor suppressor gene) levels in cancer [70]. This evidence concerns the gene TP53 and neoplasm.