What is chemoprevention: the use of medicines and natural approaches to prevent cancer?

Chemoprevention means using substances to prevent cancer from developing. It can be rendered in our language as “chemical prevention” for protection against cancer. These substances may be natural, made in a laboratory, or obtained from a living source.

Cancer begins when healthy cells change and grow uncontrollably, forming a mass called a tumor. A tumor may be malignant (cancerous) or benign. A cancerous tumor is malignant and can spread to other parts of the body (metastasis). A benign tumor means that the tumor will not spread. The transition from a healthy cell to a cancer cell usually takes years. Smoking, obesity and unfavorable lifestyle factors can affect cells’ genetic structure and trigger cancer formation (carcinogenesis).

Chemotherapy for chemoprevention is generally used by people at high risk of developing cancer. People with a higher cancer risk in this context include those with a hereditary cancer syndrome or a familial predisposition . Here chemotherapy drugs are not used to treat cancer, because there is no visible cancer, but these individuals are at high risk of developing it. However, very few chemotherapy drugs developed to treat cancer are effective for cancer prevention (chemoprevention). Indeed, using most chemotherapy drugs for this purpose may increase the risk of other cancers developing in the future or cause more resistant cancers to develop. It must therefore be emphasized that administering chemotherapy drugs for chemoprevention is a very rare practice and must always be done with a physician’s prescription.

Cancer prevention & cancer treatment

Another important point we wish to emphasize is that cancer prevention and cancer treatment are different matters . To illustrate with a few examples, it is widely known that eating a diet rich in fiber reduces the risk of colorectal cancer; conversely, fiber-rich foods have no therapeutic effect in someone who has developed colorectal cancer. Similarly, choosing cruciferous vegetables such as broccoli and cabbage in the diet may reduce head and neck cancer risk and can thus be considered within chemoprevention; however, broccoli has no role in treating head and neck cancer. Many herbal products studied under phytotherapy, probiotics, and vitamins (for example vitamin D) are in a similar situation.

Examples of chemoprevention

Here are some examples of medicines used for chemoprevention:

• Tamoxifen (Nolvadex, Tamoksifen), Raloksife (Evista): These medicines have been studied as a way to reduce breast cancer risk. They are the most effective approaches for reducing estrogen receptor-positive breast cancer risk. Estrogen receptor-positive breast cancer means that the cancer depends on estrogen to grow. Tamoxifen blocks estrogen’s effects on tumor growth. It is also among the most widely used medicines in oncology practice because it is known to reduce recurrence risk in patients diagnosed with and treated for breast cancer.
• Aspirin and other nonsteroidal anti-inflammatory drugs NSAIDs: These medicines have shown their strongest evidence for cancer prevention in colon cancer .
• Vitamin B3 – Niacin: Regular vitamin B3 use has been found effective in preventing skin cancer recurrence. However, studies were conducted in individuals who had already developed skin cancer; therefore, it is not yet clear whether taking vitamin B3 prevents skin cancer in healthy people.

Chemoprevention may delay cancer. However, someone taking a medicine for cancer prevention can still develop cancer in the future. In this respect, chemical cancer prevention may be similar to taking medicines to prevent heart disease or stroke. Examples of such medicines for cardiovascular disease include statins or blood pressure medicines, which do not offer % 100 protection.

Benefits and risks of chemoprevention

Before taking any medicine or a product marketed as natural to prevent cancer, talk with your doctor about chemoprevention’s risks and benefits. For example, medicines that may reduce cancer risk can increase the risk of side effects. People at high risk of developing cancer may be willing to accept certain side effects. Others, however, may not want to take a medicine with side effects when they are not already ill. Everyone’s preferences differ.

Talk with your doctor about your cancer risk, current health and preferences regarding taking medicines. Also ask what kind of chemical prevention might reduce your cancer risk. The effects of chemoprevention approaches seen in research studies may differ for you.

How is it determined whether a substance has chemopreventive properties?

All medicines or other substances showing evidence of reducing cancer risk are tested in clinical trials. Clinical trials are research studies involving volunteers. A chemoprevention-specific study tests a substance to assess whether it is safe for delaying or preventing cancer. Some chemopreventive effects are discovered by chance: for example, raloxifene was initially studied as a way to strengthen bones. During the research, women receiving raloxifene were found less likely to develop breast cancer.

Chemopreventive agents that work in the laboratory often fail to prevent cancer when tested in humans. Furthermore, some clinical trials have shown that certain types of chemical prevention cause serious or even life-threatening harm. For example, found in carrots, squash and similar vegetables, beta-carotene suggested in laboratory conditions that it might help prevent lung cancer. However, when tested in clinical studies, it increased lung cancer risk in people who smoked.

A clinical trial assessing, for prostate cancer, selenium and vitamin E showed that they did not reduce the risk of the disease, and there was evidence of an increase in prostate cancer among men taking vitamin E supplements.

Clinical trials generally show that products used for chemoprevention are not suitable for everyone. This is similar to other medicines used to treat cancer or prevent other diseases, such as heart disease. When evaluating chemoprevention trial results, it is also important to consider the group of participants. People participating in these trials usually have higher cancer risk, for example because they smoke or have a family history of cancer. Therefore, the study results may not apply to everyone.