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Ounce of Prevention: Cancer: Heredity, Not Destiny

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April 27, 2001
Cancer: Heredity, Not Destiny

first letter it was her last visit with us. After dinner, I remember that she remarked how much better she was feeling that day. My husband and I knew she'd been seeing doctors for a possible malignancy. Two weeks later our longtime family friend, Mary McLain, was diagnosed with pancreatic cancer. A month after that she was dead -- killed at age 76 by a disease that struck out of the blue, with no history of similar cancer in her family.

Ounce of Prevention


By Elizabeth Smoots, M.D.

Mary's story reminds me that most people who develop cancer have no special genetic predisposition for the disease. We're all susceptible to cancer, as frightening as the thought may seem. But many of us tend to forget this possibility, or simply ignore it. Worse yet, recent press about cancer-gene discoveries may be promoting a fatalistic (and fallacious) attitude about cancer: You've either got a cancer-causing gene and you're doomed, or you don't have it and you're in the clear.

I recently read an article in the New England Journal of Medicine (NEJM) that serves to dispel this popular myth. The study sheds further light on the nature-versus-nurture debate and demonstrates the importance of lifestyle choices in cancer development and prevention. An editorial accompanying the article estimates 80-90 percent of all cancers arise from factors in our environment. Fortunately, this is an area where we're in command. So shore up your defenses with ammunition from the study.

Causes of cancer

Four times as large as any previous trial, the NEJM's study of nearly 90,000 twins covered more than 10,000 cases of the most common cancers in northern Europe. Researchers reported that genetics accounted for a minority of the cancers, whereas environmental exposures caused 58-82 percent of them. (In the study, the exact number depended on the type of cancer.) They concluded that our lifestyle is the "overwhelming" contributor to cancer. This is good news for most of us.


Researchers reported that genetics accounted for a minority of the cancers, whereas environmental factors caused 58-82 percent of them. They concluded that our lifestyle is the "overwhelming" contributor to cancer.


The results do indicate that genetic factors, which we can't control, may play a significant role in certain kinds of cancer. For example, 42 percent of prostate cancer, 35 percent of colorectal cancer, and 27 percent of breast cancer in the study had a genetic component.

Even for cancers with strong hereditary ties, however, the study offers valuable insight. In people who had prostate, colon, or breast cancer, researchers found that the risk of their identical twin getting the same cancer was between 11 and 18 percent. For fraternal twins -- no more alike than ordinary siblings -- the risk was 3 to 9 percent. This indicates only a moderately increased risk among close relatives of cancer victims, the researchers say. In other words, just because you have cancer in the family doesn't mean you'll get the disease.

Prevention ideas

Family history or no, the absolute best way to prevent cancer is to replace risky lifestyle habits with healthier choices. When I talked with Mary's daughter, Susan, we uncovered several factors that may have contributed to Mary's illness. After having polio as a child, Mary developed a permanent limp that impaired her ability to exercise. She was overweight, despite a generally excellent diet. And, in the past, she had smoked for about 15 years.

The older we get, the faster the years seem to fly by. So don't put off the lifestyle changes that could improve both your quality of life and your quantity of years. Here are my top cancer-prevention picks:

  • Don't smoke.
  • Drink only in moderation.
  • Eat five to nine servings of antioxidant-rich fruits and vegetables each day.
  • Consume a plant-based diet emphasizing fiber-rich whole grains, beans, and fresh produce; go easy on animal products, fat, and salt.
  • Maintain a healthy weight. Exercise at least 30 minutes most days of the week.
  • See your provider for regular cancer-screening exams.
  • If you show warning signs of cancer, seek medical care immediately.

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Elizabeth Smoots, M.D., F.A.A.F.P., is a board-certified family physician in Seattle, Washington. A fellow of the American Academy of Family Physicians, Dr. Smoots specializes in prevention and primary care medicine.