July 12, 2000 -- You can no longer blame your parents. Most cancer is caused by environmental and lifestyle factors such as diet, smoking, drinking alcohol, and being overweight. In other words, while inherited genes do play some role in the development of certain types of cancer, the cancer prevention trump card is clearly in your hands, a new study shows. You may have more control over whether you get cancer than you think.
All of the most common cancers have both genetic and environmental components, explains Douglas Easton, PhD. In a study of nearly 50,000 pairs of twins, environmental factors accounted for 58% to 82% of the cancer risk, depending on the type of cancer. The study also showed that even when someone had a strong family history of a particular type of cancer, they were still unlikely to get cancer.
In many cancers, known lifestyle risk factors such as diet or hormone exposure explain most of the disease incidence, Easton tells WebMD. "Once genes associated with risk are identified, we should be able to work out what these genes actually do, and then work from there back to possible interactions with environmental factors.
"For example, it has been quite hard to determine what in the diet is associated with cancer risk. It seems quite likely that some of the genes associated with increased cancer risk will have functions related to [diet]. This should enable us to identify the dietary components that contribute to or reduce cancer risk," says Easton, who is director of the genetic epidemiology unit at Strangeways Research Laboratories at Cambridge University in England.
Scandinavian researchers studied the twins in the hope of discovering how much cancer risk is due to genetic factors and how much is due to other causes. Studies of twins are useful for determining whether genetic or environmental factors are more important because identical twins have all the same genes, and non-identical, or fraternal twins, share about 50% of the same genes.
If pairs of identical twins are found to be more likely have a certain type of cancer than fraternal twins, that means genetic factors are more important. If both identical and fraternal twins have about the same risk, researchers believe that genetic factors are less important and external, environmental factors are more important for that particular type of cancer.
In the study, more often than not, even when one of a pair of identical twins had cancer, the other did not develop it. "The absolute risk for the normal twin was only 3% to 9%," senior study author Kari Hemminki, MD, PhD, tells WebMD. Hemminki is professor of medicine in the department of biosciences at the Karolinska Institute in Stockholm, Sweden.
The following environmental factors already have been linked with certain types of cancer:
- Cigarette smoking/tobacco use. Smoking is by far the major cause of lung cancer worldwide, but it also increases the risk of bladder cancer and pancreatic cancer. Smoking cigarettes and using smokeless tobacco both increase the risk of mouth and throat cancer.
- Human papilloma virus. This virus is transmitted sexually and is the main cause of cervical cancer.
- Alcohol. Heavy alcohol consumption increases the risk of liver, esophagus, and throat cancer, and possibly prostate cancer.
- Dietary fat intake. Fat consumption has been associated with an increase in both colon and breast cancer.
- Low fiber and high calorie diet. It has been linked to an increase in colon cancer.
- Hormone replacement. This therapy has been linked to breast cancer with prolonged use.
- Obesity. Being obese increases the risk of uterine cancer.
Hemminki tells WebMD that the most surprising finding was that family history plays a definite, though not predominant, role in certain types of cancer. Genetic factors accounted for 42% of the risk for prostate cancer, 35% of the risk for colorectal cancer, and 27% of the risk for breast cancer.
For more information from WebMD, visit our Diseases and Conditions Cancer page.