Forget smoking, sunburns, infections, and bad diet: two-thirds of cancers are due to “bad luck.”  That was the takeaway—and subsequent media headlines—from an article published in Science last year by researchers at Johns Hopkins Unversity.

Fast forward several months and another study looking at the same question came out in Nature with the opposite conclusion: lifestyle and other external factors account for over 70% of most cancers.

Two big name journals.  Two different conclusions.  So which is right?  What should be the new takeaway?

This question of internal vs. external (or environmental) factors contributing to cancer development is of great interest to cancer investigators at the Linus Pauling Institute, as well as to public health officials everywhere.  If people believe that most of cancers are due to plain bad luck, then there’s the risk of a “why bother” attitude when it comes to things like stopping smoking, getting vaccinated, and eating vegetables.

 

But there is certainly reason to bother.  LPI researcher Gerd Bobe applauds the Science paper for shaking up the research field with a provocative new approach and spurring this conversation, but says the conclusions are overly simplistic.  Their analysis asserts that cancer risk is mostly a matter of random errors in DNA replication, rather than the influence of other factors, such as diet and lifestyle.  “It challenged the mantra of ‘take care of yourself and you’ll do better,’” he said, “but the approach was flawed.”

 

That’s why researchers at Stony Brook University, who authored the Nature paper, felt the need to set the record straight.  Using a similar approach as the original publication in Science, they designed a new model with one key difference: they assumed that the lowest lifetime risks recorded for a given cancer were due to random effects, while risks above this lower limit must be due to a combination of randomness AND environmental/lifestyle factors.  Their alternate model shows a much more significant role for external factors in the development of cancer.  The Nature authors also examined this question from three other angles and used their combined data to draw the conclusion that random DNA errors make up only 10-30% of lifetime cancer risk (a far cry from the 65% figure in the original Science article).

 

Another important point to bring to light, says LPI researcher Emily Ho, is the fact that breast and prostate cancers—two of the most common cancers in the US—are hugely influenced by environmental and lifestyle factors.  Science authors left these two cancers out of their analysis because they couldn’t find reliable data on the frequency of stem cell division in those tissues.  That said, Ho believes that both the Science and the Nature papers bring something to the table.  “Why a two-year-old develops brain cancer is baffling,” she said, “there’s no blanket statement that’s applicable here.”

 

When it comes to a takeaway message from this debate, the answer is pretty clear: the choices people make do matter. When someone reaches for a hot dog or forgoes sunscreen, these decisions add up and the body keeps track.  Lung cancer is an excellent example of the impact of lifestyle choices on cancer risk: smoking accounts for nearly 90% of lung cancer deaths. This stuff is not fully deterministic, says Ho: “There’s some luck in it, but you can change that luck in your lifetime.”

 

Eight Ways to Decrease Cancer Risk: 

• Stop smoking and avoid tobacco products
• Limit alcohol
• Protect skin from sun exposure
• Eat a diet rich in fruit and vegetables
• Avoid processed meats and limit red meat
• Maintain a healthy weight
• Be physically active
• Get vaccinated (HPV and Hepatitis B)

 

Learn more about the role of diet in cancer prevention from this webinar by LPI researcher Emily Ho. 

Learn more about cancer prevention in general from the Centers for Disease Control and Prevention and from the American Institute for Cancer Research.