A new source of cancer triggers has been discovered buried in the large expanse of DNA previously dismissed as “junk”.

Scientists highlighted “ultrasensitive” regions of non-coding DNA where even small alterations can affect many genes.

The data was used to develop a computer system called FunSeq which looks for non-coding genetic variants likely to have a big impact on human disease.

Applying FunSeq to 90 cancers – including breast, prostate and brain tumours – revealed almost 100 potential non-coding cancer drivers.

Non-coding DNA makes up 98 per cent of the human genome but, unlike genes, does not provide instructions for making proteins.

Once all non-coding DNA was thought to have no function and was written off as “junk”. Now scientists know it plays an important role in regulating the activity of our 23,000 protein-encoding genes.

Among the new discoveries was a single DNA letter change that appears to have a major impact on the development of breast cancer. The change occurs in an ultrasensitive region central to a network of many related genes.

Lead scientist Chris Tyler-Smith, from the Wellcome Trust Sanger Institute in Hinxton, Cambridgeshire, said: “Although we see that the first effective use of our tool is for cancer genomes, this method can be applied to find any potential disease-causing variant in the non-coding regions of the genome.

“We are excited about the vast potential of this method to find further disease-causing and also beneficial variants in these crucial but unexplored areas of our genome.”

The findings were published in the journal Science.