Naturally occurring substances and their role in chemo-protective effects.

Cancer chemoprevention is defined as the use of natural, synthetic or biological chemical agents to reverse, suppress or prevent carcinogenic progression of invasive cancer. Carcinogenesis is a complex multi-step process; therefore, it is necessary to attack cell proliferation, stimulate apoptosis and inhibit angiogenesis. There have been more than 60 randomised trials using chemopreventive potential agents. The success of several recent clinical trials in preventing cancer in high-risk populations suggests that chemoprevention is a rational and appealing strategy. In this review, we describe the conceptual basis for the chemoprevention of cancer, proven concepts of efficiency and current trends in the use of chemopreventive agents according to place and mechanism of action. We classify chemopreventive substances into seven groups based on their chemical structure and their effects, namely, deltanoids (paracalcitriol), retinoids (13-cis retinoic acid), non-steroidal anti-rheumatics (Deguelin), antiestrogens (genistein), polyphenols (curcumin), sulphur containing compounds (sulforaphane) and terpenes (lycopene). Chemoprevention is one of several promising strategies for reducing the incidence of malignant tumours or helping to prolong the time before recurrence.