24/03/2017 14:02 GMT

Two Thirds Of Cancers Are Caused By 'Back Luck', Not Lifestyle Choices

'It's not your fault.'

They say life isn’t always fair, but there are few things that seem quite as cruel as a potentially-deadly cancer diagnosis for someone who has followed all the rules of healthy living.

After spending a life not smoking, eating a healthy diet, exercising and avoiding anything that might increase their risk of the disease, it leads many patients to ask the inevitable ‘why me’?   

Now, a new study has shown that up to two-thirds of cancers are caused by random mistakes in our DNA and “will occur no matter how perfect the environment”, says assistant professor Cristian Tomasetti

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Winning the cancer lottery it seems, is partially due to the roll of the dice and getting lucky, as our DNA makes ‘mistakes’ and copy errors during duplication, which leads to the long-term problems.

Tomasetti, from the John Hopkins Kimmel Cancer Centre, said: “It is well-known that we must avoid environmental factors such as smoking to decrease our risk of getting cancer. But it is not as well-known that each time a normal cell divides and copies its DNA to produce two new cells, it makes multiple mistakes.

“These copying mistakes are a potent source of cancer mutations that historically have been scientifically undervalued, and this new work provides the first estimate of the fraction of mutations caused by these mistakes.”

According to the researchers, it generally takes two or more critical gene mutations for cancer to occur. In a person, these mutations can be due to random DNA copying errors, the environment or inherited genes. 

Depending on the type of cancer, the likelihood of each cause varies. For example, in lung cancer 5%of all the mutations are due to environmental factors, mostly smoking, and 35% are due to DNA copying errors.

In cancers of the prostate, brain or bone, more than 95% of the mutations are due to random copying errors.

Approximately 40% of cancers can be prevented by avoiding unhealthy environments and lifestyles, so public education should still focus on avoiding these environmental agents.

However populations need to understand that it is inevitable more people will develop cancer due to these random mistakes being made at a cellular level.

Bert Vogelstein, co-director of the John Hopkins Kimmel Cancer Centre, said people who suffer from random mistakes should be comforted in knowing they couldn’t have done anything differently: “It’s not your fault. Nothing you did or didn’t do was responsible for your illness.”

How comforting.