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Chemoprevention - The Best Approach to Cancer?

© David Olle

Why is chemoprevention of cancer important?

Although great strides have taken place in the understanding and treatment of cancers, it would be much more preferable to prevent cancer rather than to treat it. The transformation of normal cells into cancerous ones is a long multistep process that can take many years. 1The cancer process begins with initiation, which is a genetic change in the cell's DNA molecule. The body has complex mechanisms in place to repair the damaged DNA, so the vast majority of damaged cells do no not progress to cancer. Chemoprevention is the use of natural or synthetic compounds to intervene in the early stages of the cancer process in an attempt to prevent the cells from becoming malignant (carcinogenic). Chemoprevention should not be confused with chemotherapy, which is the use of chemical compounds to preferentially kill cancer cells to prevent the further progression of the cancer.

Who should consider the use of chemoprevention?

Everyone can practice chemoprevention as it relates to dietary sources of these compounds. 2Phytochemicals are nonnutritive plant chemicals that may have protective, disease preventing properties. Thousands of phytochemicals have been identified in fruits, vegetables, grains and seeds. The protective action of phytochemicals has been largely deduced from epidemiological studies. In these cases, researchers attempt to equate the cancer incidence in a select population based on the consumption of certain foods and the phytochemicals they contain. Laboratory studies have determined the mechanisms by which many phytochemicals exert their protective effects. However, it can be difficult to relate this understanding to the consumption of certain foods. Each food involves the consumption of many phytochemicals, and the observed reduction in disease incidence may very well be due to other factors. In any event, the studies do provide direction in understanding the beneficial effect of eating phytochemicals in plant products.

In order to demonstrate a cause and effect relationship between the use of a chemoprevention agent and a reduction in cancer incidence, the scientific community requires the use of well-controlled clinical trials. The study groups are designed to be as uniform as possible, except for the test compounds. This requires the isolation of the chemoprevention agent from natural foods, or to prepare synthetic ones in the laboratory. As described below, synthetic compounds similar to Vitamins A and D can be administered at higher potencies than are found in foods, so can be more effective as chemoprevention agents.

There are ethical issues involved regarding which individuals should enter into chemoprevention clinical trials; and if the agents are found to be effective, who should receive them. 4It must be remembered that the individuals in question are basically healthy and show no clinical signs of cancer. The attendant hardships, inconveniences and possible toxicities associated with the use of these compounds are more easily justified for patients who already show symptoms of cancer. The current consensus in the medical community is that only those individuals with an increased risk for developing cancer should receive chemoprevention. Risk factors could include a family history of the cancer, belonging to a certain population group that is more susceptible, or a premalignant histologic change found on biopsy. The individual may avoid cancer without chemoprevention intervention, or may still develop cancer with the intervention.

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