A 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 cancer susceptibility is associated with
• environmental carcinogens and
• 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.
Yet a recent study gives a far more plausible explanation that is linked to diet, an environmental factor. This study shows that bacteria associated with colon cancer live in your colon and manufacture biofilms that they use to prevent your immunity from killing them. These biofilms are associated with increased risk for colon cancer and are not regularly found in the small intestine. We do not yet know all of the reasons why some cancer cells are destroyed by your own body and others go on to become cancers, but I think it is more reasonable to state that bacterial biofilms in the colon cause colon cancer than it is to state that the high number of random mutations in the colon cause colon cancer. The random mutation theory also does not explain why mice, which have the highest rate of cell reproduction, do not have the highest rate of cancers or why blue whales, which have the largest number of cells of any organism, have a low cancer rate.
Why Cancer is More Likely to be Caused by Environmental or Genetic Factors
The researchers only set up a mathematical model that associated rates of cancer with rates of cell division. They did not study people and they did not study environmental or genetic causes of cancers. To show that cancer is caused by random chances of gene mutation, they would have had to study how environmental and genetic factors affect gene mutations. Since they did not do this, they have to state only that their conclusions are their opinions and are not supported by adequate data on lifestyle and genetic factors. They have shown what we already know, that SOME cases of cancer are caused by random gene mutations. I believe that we will find that the majority of cases of cancer are associated with
• genetic cancers that run in families,
• unhealthful lifestyles, and
• exposure to factors that cause cancer,
and that the more of these factors a person accumulates over a lifetime, the greater the cancer risk.
Many studies show that people with the same genes are subject to higher rates of cancer (and other diseases) when they leave a healthy native lifestyle behind and adopt a more hazardous one. Many studies show that some societies have fewer cancers apparently because they avoid certain carcinogens. For example, Seventh Day Adventists, who are vegetarians with no exposure to meat or other animal products over their lifetimes, have much lower rates of colon cancer than other North Americans.
Some cancers, such as those in the lung and skin, are too common to be caused just by random cell mutations from their rates of stem-cell division. Smoking causes the increased rate of lung cancer and excess sunlight exposure accounts for the increased rate of skin cancers. The rate of lung cancer in smokers is very high and exposure to toxic chemicals is a potent cause of cancers.
The authors did not include data on thyroid, breast or prostate cancers because they did not fit into their model. If they had, they would probably have found that these cancers are predominantly caused by genetic and environmental factors. Breast cancer is associated with genetic factors because it runs in families and many of these genetic risk factors for breast cancer are well known. Some forms of thyroid cancer run commonly in certain families. Breast cancer is also associated with taking the female hormones, estrogen and progesterone, drinking alcohol, being overweight, and so forth. Prostate cancer appears to be primarily an environmental disease since virtually 100 percent of North American men develop it by age 90, compared to two percent of rural Chinese men (Cancer Biol Med, Jun 2012; 9(2): 128–132).
You can play an active role in preventing cancer by avoiding the lifestyle habits and environmental toxins that have been linked to cancers, such as:
• Lack of exercise
• Poor diet (too much red meat, sugared drinks, sugar-added foods, fried foods ; too little fruits and vegetables)
• Lack of vitamin D
• Excessive sun exposure
• Sexually transmitted diseases (infectious agents associated with cancers that can be spread through sexual contact include HPV, Hepatitis B, Hepatitis C, Epstein-Barr Virus (mono), Human herpes virus 8 (HHV-8), Human T-lymphotrophic virus-1 (HTLV-1), Merkel cell polyomavirus (MCV), Simian virus 40 (SV40), Helicobacter, chlamydia and many more)
• Agent Orange
• Tetrachlorethylene cleansing fluid
• Air pollution
• Radiation including X-rays
• Hormone replacement therapy
• Drugs to suppress immunity
This is just a partial list of lifestyle and environmental factors that have been linked to various types of cancers. It appears that the more of these exposures you have over a lifetime, the greater your risk for cancers.