In an earlier study, Bert Vogelstein, from Johns Hopkins University, and colleagues argued that random DNA errors that happen when self-renewing cells divide can be blamed for the development of some cases of cancer.

Now in a new study, the researchers showed how these unlucky mutations play a more significant role in the development of cancer than environmental, hereditary or lifestyle factors by providing for the first time the percentage of cancer mutations that is due to the latter three as well as random chance.

Why People With Healthy Lifestyle Still Develop Cancer

The researchers found that in general, 66 percent of the genetic mutations that went on to become cancer are due to simple random errors that occur when the cells replace themselves.

The findings showed that these bad luck mutations are the biggest cause of cancer when compared with other factors. Environmental factors contribute 29 percent and the remaining 5 percent are inherited.

"Every time a perfectly normal cell divides, as you all know, it makes several mistakes -- mutations," explained Vogelstein. "Now most of the time, these mutations don't do any harm. They occur in junk DNA, genes unrelated to cancer, unimportant places with respect to cancer. That's the usual situation and that's good luck."

Many people who engage in healthy practices such as eating a healthy diet and not smoking still develop cancer. The findings of the study offer one reason why despite having healthy lifestyles, some people have DNA mutations that lead to cancer.

Healthy Lifestyle Still Matters

Despite the findings, the researchers still stressed the importance of healthy living. Some cancers are driven by avoidable factors. Vogelstein, for instance, said that the study does not contradict the generally accepted wisdom that most cases of lung cancer cases are preventable.

Men who smoke have 23 times increased risk to develop lung tumors than their counterparts who do not smoke, and women smokers have 13 times increased chances than women who do not smoke.

Cigarette smoking can lead to more genetic mutations than what can normally happen and just like random mutations, smoking-related mutations can either affect the cancer-driving genes or DNAs that are not relevant to cancer.

While cancers affecting tissues that frequently divide such as colon cancer may have high input from chance mutation, diet, smoking and engaging in physical activities have roles in the development of the cancer as well.

The researchers likewise said that the findings of the study fit well with the general advice that 40 percent of all cancers are preventable if people eat plenty of fruits and vegetables, exercise on a regular basis, avoid red meat, do not smoke ,and stay away from harmful UV rays such as those that come from tanning beds and sunlight.

"Primary prevention is the best way to reduce cancer deaths. Recognition of a third contributor to cancer — R mutations — does not diminish the importance of primary prevention but emphasizes that not all cancers can be prevented by avoiding environmental risk factors," the researchers wrote in their study published in the journal Science.

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