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We all know certain behaviors like smoking can increase your risk of cancer. But can all cancers be linked either to something we did or some factor we inherited?
The surprising answer for many types of cancer appears to be “no” according to a recent article published in the journal Science and reported in The New York Times.
Researchers Dr. Cristian Tomasetti and Dr. Bert Vogelstein of Johns Hopkins University School of Medicine reported that random genetic mistakes or basic bad luck may be responsible for the risk of up to two-thirds of many types of cancer.
That means environmental factors and genetic inheritance may be to blame for only one-third of certain types of cancer cases.
Tomasetti, an applied mathematician, said, “This was definitely beyond my expectations. It’s about double what I would have thought.”
To reach their conclusion, the research team developed a statistical model using known rates of cell division in 31 different types of body tissue. They omitted breast and prostate cancers due to insufficient data on the rate of cell division for those tissue types.
As cells wear out, specialized cells known as stem cells divide to create replacement cells for that specific type of tissue. Stem cells are unique because they are able to divide or replicate themselves many times.
When stem cells divide, they duplicate their own genetic code to create a new cell. Mistakes in the code duplication process can cause uncontrolled growth of those cells, resulting in cancer or a tumor.
The researchers used recently available advances in stem-cell biology to investigate observations made more than 100 years ago that had never been fully explained. Historically, scientists knew that some types of body tissue are at much higher risk to develop cancer than other types of tissue. But they didn’t know why.
For example, cancer is 24 percent more likely to develop in cells in the large intestine than in the small intestine.
The Johns Hopkins researchers determined that large intestine tissue contains many more stem cells than small intestine tissue. They also noted that cells in the large intestine needed to be replaced much more often than in the small intestine.
So there is an apparent correlation between more frequent cell replacement and higher risk of cancer because there are more frequent opportunities for errors to develop in the cells’ genetic code.
In other cases, known environmental factors such as smoking for lung cancer, or sun exposure for skin cancer, can drive up the risk of developing that cancer. Still other cancer risks can be significantly increased by inheriting a known cancer-causing gene.
Tomasetti compared the risk of cancer to the risk of having a car accident. Taking a long car trip increases the risk of being in an accidental car crash — the bad luck example.
Driving a car with defective brakes or driving in snow makes that risk even higher. This correlates to adding a behavior such as smoking or an environmental risk such as sun exposure on top of the “bad luck” factor.
The researchers see their discovery as both good and bad news, depending on your perspective.
Referring to patients who may wonder if they unknowingly did something to bring on their cancer, Tomasetti sees the results as comforting.
Vogelstein believes the report is good news for many people who do not have cancer. While people should still be aware of known behaviors that can increase their cancer risks, they may feel less worried about every action or food choice they make.
But for people who do not have cancer and who prefer to be in control of everything they can, the researchers believe the report will be perceived as bad news and a potential source of fear.
Dr. Kenneth Offit, chief of the clinical genetics service at Memorial Sloan Kettering Cancer Center in Manhattan, said that the hypothesis “appears to be correct”.
But he also noted that not all cancers follow the model in the report. For example, some cancers have a significantly higher hereditary component than the new study suggests.
Offit emphasized the importance of continuing to stress important public health awareness messages and stated that approximately half of all cancer deaths could be avoided.
Offit said, “Although most cancer is likely due to random events (affecting DNA replication) at the cellular level, at the population level, the most powerful interventions to decrease the burden of cancer are to stop smoking, know your family history and aim for ideal weight.”
Since so many cancer cases are the result of random genetic mistakes that cannot be predicted or prevented, Tomasetti and Vogelstein believe their research points to a need to develop better tests for early detection of cancer so it can be more effectively treated.
Sources:
The New York Times. Cancer’s Random Assault. Denise Grady. Web. February 25, 2015.
http://www.nytimes.com/2015/01/06/health/cancers-random-assault.html?_r=1
National Institutes of Health. Stem Cell Basics. Web. February 25, 2015.
http://stemcells.nih.gov/info/basics/pages/basics1.aspx
Reviewed February 26, 2015
by Michele Blacksberg RN
Edited by Jody Smith
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