Most cancers are caused by random mistakes in the genetic code when cells divide out of the blue, new research shows.
Despite widespread belief that the disease is usually inherited or triggered by an unhealthy lifestyle, two thirds of cases can be put down to DNA errors.
And there is nothing that can be done to prevent it from happening – it’s simply down to bad luck, scientists claim.
Cancers triggered by copying errors could occur ‘no matter how perfect the environment’, researchers from Johns Hopkins Kimmel Cancer Center warn.
The findings explain why cancer often strikes people who follow all of the rules of healthy living and have no family history of the disease.
Study author Dr Cristian Tomasetti 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
The researchers compared DNA copying errors to ‘typos’ in a written manuscript.
Dr Bert Vogelstein, also involved in the research, said:
You can reduce your chance of typographical errors by making sure you’re not drowsy while typing and that your keyboard isn’t missing some keys.
But typos will still occur because no-one can type perfectly.
The researchers studied mutations that drive abnormal cell growth in 32 different types of cancer.
Using DNA sequencing and a collection of data, they developed a mathematical way to assess the role of genetic copying errors.
The results showed that it generally took two or more critical gene mutations to trigger the disease.
In some cancer types, such as those affecting the prostate, brain and bone, more than 95 per cent were due to random DNA copying errors.
Copying mistakes were linked to 77 per cent of pancreatic cancers but only 35 per cent of lung cancers.
The latter was mostly triggered by smoking and other environmental factors, according to the study published in the journal Science.
Overall, 66 per cent of cancer mutations resulted from copying errors, 29 per cent from lifestyle factors, and just five per cent from inherited faulty genes.
Dr Vogelstein added:
We need to continue to encourage people to avoid environmental agents and lifestyles that increase their risk of developing cancer mutations.
‘However, many people will still develop cancers due to these random DNA copying errors, and better methods to detect all cancers earlier, while they are still curable, are urgently needed.
Professor Mel Greaves, of The Institute of Cancer Research in London, said:
Even if, as this study suggests, most individual cancer mutations are due to random chance, the researchers admit that the cancers they cause may still be preventable.
We have good evidence to show that cancer is caused by a complex mix of environmental exposures, inherited risk, and random chance.
And while the genes we inherit from our parents are unreturnable and many chance events are non-negotiable, fortunately for us, exposures are major contributors to our risk of cancer and offer a route to risk reduction or prevention