Friday, October 23, 2020

Chemoprevention – The Answer to Cancer?


Recently, you may have heard the words chemoprevention, nutraceuticals, and phytochemicals in the media. What exactly do these terms mean? With the ever-increasing interest in improving our health, it is important to understand these words and understand their function in health care. The information presented here will provide a basis for deciphering the mixed messages that are being delivered in the media, conversations, research, and education.

Research has demonstrated that cancer is a largely avoidable disease. It is estimated that more than two-thirds of cancer may be prevented through lifestyle modification (1). Nearly one-third of these cancer occurrences can be attributed to diet alone, secondary to our American diet of high-fat, low-fiber content. Fruit and vegetable consumption have been consistently shown to reduce the risk of many cancers (2). A major prevention strategy has been the “5 A Day for Better Health” program sponsored by the National Cancer Institute (NCI), encouraging the public to include more fruits and vegetables in their diet.

The American Cancer Society has developed guidelines for nutrition and cancer prevention. These guidelines are similar to the Dietary Guidelines for Americans and include the following:

  • Choose most of the foods you eat from plant sources.
  • Limit your intake of high-fat foods, particularly from animal sources.
  • Be physically active. Achieve and maintain a healthy weight.
  • Limit consumption of alcoholic beverages if you drink at all.

Consequently, even before these guidelines were developed, researchers began investigating several substances that have the potential to inhibit cancer tumor formation. This investigation evolved into what is called “chemoprevention” today. The “chemoprevention” strategy of preventing cancer was founded in the mid 1970s by Michael B. Sporn, an innovator in cancer prevention research (3). Successful trials involving chemopreventive agents and animals led scientists to design larger similar trials with humans. In fact, in 1995 the NCI alone sponsored more than 50 trials of 25 different compounds (4). These chemical compounds along with several others are currently being recognized for their potential to prevent and treat various types of cancer.

This fact sheet will explain the concept of chemoprevention, list agents used in chemoprevention, and describe benefits of chemoprevention in regard to cancer prevention and treatment.

Current “Buzzwords” in Nutrition
Chemoprevention — Using one or several chemical compounds to prevent,
stop, or reverse the development of cancer.
Designer Food — Processed foods that are supplemented with food
ingredients naturally rich in disease-preventing substances (5).
Functional Food — Any modified food or food ingredient that may provide
a health benefit beyond the traditional nutrients it contains (6).
Nutraceutical — Specific chemical compounds in food, including vitamins
and additives, that may aid in preventing disease.
Pharmafood — Food or nutrient that claims medical or health benefits,
including the prevention and treatment of disease (7).
Phytochemical — Nonnutrient plant chemicals that contain protective,
disease-preventing compounds.

What is chemoprevention and how does it work?

Chemoprevention is the attempt to use natural and synthetic compounds to intervene in the early stages of cancer, before invasive disease begins. This strategy is involved in the process of carcinogenesis — the transformation of a normal cell into a cancer cell. Currently, the NCI has made chemoprevention research a top priority; more than 400 potential agents are currently under investigation (8).

Chemopreventive agents can act in two ways: they can prevent or stop genetic mutations that lead to cancer, and they can prevent or stop processes that lead to excessive replication of damaged cells.

Chemoprevention should not be confused with chemotherapy. Chemotherapy’s aim is to kill cells, particularly cancer cells, in the hope of preventing further cancer progression. Chemoprevention, on the other hand, involves administering nontoxic agents to otherwise healthy individuals who may be at increased risk for cancer.

Agents most commonly used in chemoprevention

An agent must have minimal short-term and no known long-term toxicity. It must be highly effective, easy to administer, and be inexpensive (9). Food, a readily available item, contains several promising chemopreventive compounds such as certain vitamins, minerals, and phytochemicals. See the table below to find out more about these agents.

AgentAgent typeCancer prevention/treatment
Vitamin A +
other retinoids
vitamin skin, head + neck, & lung
Vitamin C vitamin colon & stomach
Vitamin D vitamin colon
Vitamin E vitamin lung, head + neck, colon, & stomach
Folic Acid vitamin precancerous cells of the cervix
Selenium mineral skin
Calcium mineral colon
Beta-Carotene phytochemical lung, head + neck, colon & stomach
Monoterpenes phytochemical breast
Tamoxifen drug breast
Finasteride drug prostate
Oltipraz drug liver
drugs — aspirin,
drug colon
Sunscreen other skin
(blue-green algae) other head + neck

Why do we do chemoprevention trials?

A potential chemopreventive agent goes through several phases before it can be administered to large numbers of people. These phases determine the chemopreventive agent’s effectiveness, dose toxicity, and side effects. An agent starts in Phase I and continues to advance to Phase III as long as it is acceptable within specific guidelines. After an agent passes through Phase III, data is collected from the trial and then recommendations regarding the agent begin to be studied in further detail. It may take several years before an agent passes through all the phases and is recommended to individuals who have increased risk of developing cancer. The different phases are described in detail here:

Phase I: Involves 25-100 people, lasts less than one year, and studies dose toxicity and side effects of the agent in humans.

Phase II, IIb: Involves 100-1,000 people, lasts one to five years, studies the agent for effectiveness.

Phase III: Involves 1,000-10,000 people, lasts five to 10 years, determines the agent’s effect on cancer incidence, and pays close attention to long-term side effects (10).

Examples of promising chemoprevention

Phase III trials (11)

Breast Cancer Prevention Trial (BCPT)

Studying the effect of the drug tamoxifen on the reduction of breast cancer rates in women at high risk or older than 35 years. Result(s): Study is on-going, but recent results indicate promising effects.

Isotretinoin Efficacy Trial

Studying the effect of the retinoid isotretinoin on secondary cancerous tumors in the head and neck of high-risk people who had been initially treated for head and neck cancer. Result(s): 83% decrease in secondary tumors of head and neck.

Linxian General Population Trial

Studying the effect of four combinations of vitamins and minerals on reducing esophageal and stomach cancer in high-risk people. Result(s): 21% decrease in stomach cancer deaths for people taking beta-carotene, vitamin E, and selenium.

Prostate Cancer Prevention Trial (PCPT)

Studying the effect of the drug finasteride on prostate cancer risk in men ages 55 and over. Result(s): Results to be expected within four to five years.

How is chemoprevention beneficial?

The ultimate goal of chemoprevention is the reduction of cancer incidence. Approximately 550,000 people in the United States were expected to die of cancer in 1996 (12). In fact, 1.4 million new cancer cases occur each year in the United States. If chemoprevention can prevent one or even 1,000 occurrences of cancer without complications, it can be deemed successful. The individuals that are targeted include people with lifestyle risks such as smoking or a high-fat diet, people with a family history of cancer, people at high risk because of a precancerous condition, and people who have had cancer and are at risk for a second cancer.

Are there any drawbacks of chemoprevention?

Even though many chemopreventive agents are naturally found in food, they are administered at high doses that can possibly produce unfavorable side effects. Short- and long-term side effects of chemopreventive agents are unknown at this time.

Although most chemoprevention trials show promising results, there are a few that present possible detrimental effects. One study, the Alpha-Tocopherol, Beta-Carotene Lung Cancer Prevention Study, tested daily doses of alpha-tocopherol (vitamin E) or beta-carotene, or both, on reducing the rates of lung and other cancers in male smokers. One of the findings included an 18% increase in lung cancer in the beta-carotene group. This result stresses the importance of waiting for conclusive results and approved recommendations from the scientific world before making any lifestyle changes.


There is little evidence supporting widespread use of chemopreventive agents in the entire population. The evidence only supports risk reduction for those individuals at risk for cancer. At this time, the NCI does not recommend supplements of vitamins, minerals, or other agents for the prevention of cancer. It does recommend eating a well-balanced, low-fat diet including fruits, vegetables, and grains.

Chemoprevention is not simple, and successes may not come quickly. However, for individuals at high risk for cancer and possibly the general population in the future, chemoprevention has the potential of providing an important means for cancer risk reduction (13).

As with any health recommendation, it is advisable to consult your health-care provider before making any lifestyle changes. This fact sheet should not in any way replace the advice of your physician.

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