The answer seemed to be “yes”, earlier this year based on several news reports1,2,3 citing a cancer study published by Science4. The news claimed that two thirds of cancer cases are due to random bad luck. My immediate feeling was of relief; I thought that, since bad luck is the major player in cancer development, there is little sense in prevention. But on second thought, I wondered why cancer researchers would make such claims and how they reached those conclusions in the first place?

Next, I did something that I suspect not everyone does; I went to the primary source – the science article itself. Now I must admit, even as a cancer researcher this article took a lot of mental effort to understand, and I can see how the media may have gotten it wrong. Here’s a few questions I wanted to answer…


This paper was written by two Johns Hopkins5 researchers who wanted to understand why cancers arise more frequently in certain body tissues (i.e. the colon) when compared to others (i.e. the brain).


In the study, they looked at 31 types of cancer (there are actually over 200 different types!) and compared the possibility – or risk – of getting those cancers to the number of times a stem cell divides within that same type of tissue. The researchers looked at stem cells because they are cells that (i) have long lives, (ii) renew themselves, and (iii) are responsible for generating and maintaining all the other cells in our tissues. Since they have a long life, they are more likely to accumulate detrimental changes in their genetic code, when compared to cells with a short life – those that make up the bulk of our organs.


The researchers found that tissues whose stem cells divided more frequently were more likely to be sources of cancer, than tissues whose stem cells did not divide as often. In addition, the researchers found that the number of times stem cells divide largely explained differences in the risk of developing cancer, among the 31 types studied. In fact, the number of times stem cells divide could explain approximately two thirds of the possibility of getting cancer in one tissue versus another. Another important point of the study is that some tissues (i.e. the lung) have a high cancer risk, even though their stem cells do not divide very frequently. This shows that aside from number of cell divisions, both environmental (i.e. smoking) and inherited factors can play an important role.


What this study actually tells us is that a significant proportion of cancers happen due to random genetic changes, but that lifestyle and hereditary factors DO play a role. These findings are in direct contrast with the reports in the media, which attributed bad luck as the cause of two thirds of cancers and suggested that we are powerless to prevent cancer. As you can see, it is essential to clarify what these findings mean for the general public, because “sensational headlines” have great power in influencing our behaviour. Although some cancers can occur at random, maintaining a healthy lifestyle and avoiding risky behaviours such as smoking or sun exposure, greatly impact our chances of preventing cancer. Finally, if even with prevention we are struck by “bad luck” and end up developing cancer, it is key to rely on early detection to target tumors that have not yet progressed to more aggressive stages.

This article was written by Natalia Ruiz. Natalia obtained a Master of Science degree from the University of Toronto studying the most aggressive and metastatic forms of breast cancer. To find out more about Natalia and her research check out her bio on the Members page.


  1. CBC News: http://www.cbc.ca/news/health/two-thirds-of-cancers-caused-by-bad-luck-not-heredity-environment-1.2888125
  2. Yahoo News: http://news.yahoo.com/cancer-often-due-bad-luck-not-genes-environment-215201393.html
  3. BBC News: http://www.bbc.com/news/health-30641833
  4. Tomasetti C. and Vogelstein B. (2015) Variation in cancer risk among tissues can be explained by the number of stem cell divisions. Science, 347(6217):78-81

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