An international team of scientists is reporting a significant milestone for cancer research after charting 21 major mutations behind the vast majority of tumors.

The disruptive changes to the genetic code, reported in Nature, accounted for 97% of the 30 most common cancers.

Finding out what causes the mutations could lead to new treatments. Some causes, such as smoking are known, but more than half are still a mystery.

A tumor starts when one of the building blocks of bodies, a cell, goes wrong. Over the course of a lifetime cells pick up an array of mutations which can eventually transform them into deadly tumors which grow uncontrollably.

The international team of researchers was looking for the causes of those mutations as part of the largest-ever analysis of cancer genomes.

Cancer researchers charted 21 major mutations behind the vast majority of tumors

The well-known ones such as UV damage and smoking mutate the DNA, increasing the odds of cancer.

But each also leaves behind a unique hallmark – a piece of “genetic graffiti” – that shows if smoking or UV radiation has mutated the DNA.

Researchers, led by the Wellcome Trust Sanger Institute in the UK, hunted for more examples of “graffiti” in 7,042 samples taken from the 30 most common cancers.

The found that 21 separate “graffiti signatures” could account for 97% of the mutations which led to cancer.

Other signatures were related to ageing and the body’s immune system. Cells respond to viral infection by activating a class of enzymes which mutate the viruses until they can no longer function.

However, 12 of the signatures defy explanation for now.

It is hoped that if some of them can be pinned down to things in the environment then new ways of preventing cancer could be developed.

It may also spur further research. One of the unknown causes of mutation happens only in neuroblastoma, a cancer of nerve cells which normally affects children, so something unique is happening there.

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