Natural Defenses Against Cancer - Chapter 1 Introduction To Preventing Cancer: Cancer

Content provided by the Faculty of the Harvard Medical School

Natural defenses against cancer

Fortunately, people have inborn mechanisms to protect cells and keep them healthy. These include the immune system, tumor suppressor genes, and antioxidants.

The immune system. The immune system consists of a wide array of cells that in various ways provide for defense against invaders. Some function like sentries, sounding the alert. Others are soldiers, mounting the attack once an invader, such as a virus, has been identified.

Many scientists now believe that the immune system does defend the body against cancer, at least initially. This view is buttressed by studies that show that a cancer can sometimes be detected microscopically, as in the case of some prostate cancers, but is too small to be seen otherwise. At this stage, a cancer may be growing so slowly that it produces no symptoms. The theory is that the immune system is holding the cancer at bay.

This could explain why a faulty immune system can lead to a higher cancer risk. For instance, people who receive a kidney transplant and need to take medications to suppress their immune system have a higher risk of certain cancers. Two major studies found that total cancer incidence after kidney transplants was more than double the expected rate amongst Canadian, Australian and New Zealander patients. Cases of lip cancer were over 30 times higher than expected after transplants; non Hodgkins Lymphoma rates were almost nine times higher; and kidney cancers were over seven times higher. People with advanced HIV infection, whose immune systems are rendered nearly helpless, appear to experience elevated cancer risks similar to those of kidney transplant patients.

Researchers speculate that cancer cells are able to elude detection by the immune system. Another theory holds that external factors - such as depression, stress, or immunosuppressive medications - can sufficiently dampen the immune response so that it is not able to hunt down and destroy cancer cells.

Tumor suppressor genes. Yet another defense system against cancer takes the form of tumor suppressor genes. Just as oncogenes make a cell more vulnerable to factors that can turn it cancerous, tumor suppressor genes squelch those cancerous tendencies, so the cell does not cross the line from damaged to malignant. Tumor suppressor genes are sometimes described as molecular versions of brakes because they literally put a stop to the uncontrolled cell growth and proliferation that is characteristic of cancer.

Antioxidant protection. Finally, antioxidants provide a way to counter the damage done by free radicals. Antioxidants can take the form of nutrients consumed from food or enzymes made internally by the body. Some antioxidants neutralize free radicals, so they are not so volatile and prone to raid healthy cells. Others counter the destructive effects of free radicals by literally repairing the damage. Still others interfere with the chemical process that some carcinogens must go through before they are able to wreak havoc on healthy cells. The best way to increase antioxidant levels in your body is to eat more fruits and vegetables.

Four Defensive Strategies The cell has a surprising array of defense mechanisms to protect it from damage. Immune cells in the bloodstream, such as lymphocytes, attack viruses that cause cell mutation. Tumor suppressor genes, the body's natural mechanism for cell death, cause cells with mutated DNA to die. Antioxidants can neutralize the dangerous free radicals before they damage DNA. Still other antioxidants interfere with carcinogens that enter the body before they can wreak havoc on healthy cells.

From biology to behavior

One of the guiding theories of cancer prevention is that making changes in your behavior - including diet and lifestyle - will boost your biological defenses and protect your cells from the sorts of injuries that lead to the spread of cancer. Avoiding toxic substances such as cigarette smoke, for instance, will reduce your exposure to significant initiators of cell damage. Eating a diet with plenty of fruits and vegetables will give you antioxidants to help counter those disruptive free radicals.

Weight also appears to play an important role. A diet that keeps calories in line can also discourage weight gain, a demonstrated cancer risk factor, while encouraging weight loss-an established cancer prevention tool. Even modest weight fluctuations are important. Data from the Women's Health Initiative suggests that as little as six pounds gained or lost in adult women can raise or lower, respectively, breast cancer risk. But the risk appears to be linear: the more excess weight you shed, the more protected from breast cancer you become; the more weight you gain, the more likely you are to get cancer.

The bottom line is that there is seldom one event that causes cancer - and seldom one way to protect yourself. Cancer protection, like cancer itself, is a multi-step process.

Last updated:	May 01, 2008