A recent study from respected researchers at Johns Hopkins claims that two-thirds of adult cancers are caused by random DNA mutations in your cells, and far fewer cancers are caused by genetics, lifestyle or exposure to cancer-causing agents (Science, January 2, 2015). If this is so, changing your lifestyle or limiting exposure to carcinogens would do little to prevent cancer, yet the scientific literature overwhelmingly shows that the following determine cancer susceptibility.
- Lifestyle
- Environmental carcinogens
- Genetic factors
How the Study was Done
The Johns Hopkins researchers set out to explain why some tissues are more likely to develop cancer than others. They reviewed the scientific literature for the number of stem cell divisions of 31 different tissue types. Stem cells are basic cells that turn into specific tissues such as lung, skin, or heart muscle. Dividing cells must make copies of their DNA, and mutations in the DNA can cause uncontrolled growth that is cancer. The authors claim that the more often tissue cells divide to form new cells, the more likely they are to form mutations that increase cancer risk.Why I Disagree with Their Message
Scientists have known for more than 50 years that humans produce millions of cancer cells every day. Virtually all cancer cells are searched out by a person’s immunity and destroyed before they can cause cancer. Why wouldn’t it be reasonable to conclude that factors in the environment impair immunity to allow the cancer cells to live, or make cancer cells more resistant to a person’s immunity?The authors support their theory of random genetic mutations causing cancer by giving the example that the colon has a lifetime cancer risk of 4.8 percent that is 24 times higher than in the small intestine, where it is 0.2 percent. The scientists found that the large intestine has many more stem cells than the small intestine, and that they divide more often: 73 times a year, compared with 24 times.