U.K. study reveals how ionizing radiation damages DNA, increasing cancer risk

Researchers in Britain say they have discovered how ionizing radiation — such as gamma rays or X-rays used in nuclear medicine — leaves behind a molecular fingerprint in certain human cancers.

X-rays leave characteristic patterns of 'mutational signatures'

A nuclear medicine technologist prepares a patient for a gamma camera to take body images. (Canadian Press)

Researchers in Britain say they have discovered how ionizing radiation — such as gamma rays or X-rays used in nuclear medicine — leaves behind a molecular fingerprint in human cancers.

It's already known that ionizing radiation can cause DNA damage, increasing the risk of developing cancer.

But now, researchers at the Wellcome Trust Sanger Institute say they have been able to identify two characteristic patterns of damage.

The damage is known as a mutational signature left on the genome of a cancer cell.

The researchers looked for mutational signatures in 12 patients with secondary radiation-associated tumours, comparing these with 319 patients with tumours (284 breast cancers and 35 osteosarcomas) who had not been exposed to radiation.

"To find out how radiation could cause cancer, we studied the genomes of cancers caused by radiation in comparison to tumours that arose spontaneously," Peter Campbell, who led the study, said in a release.

2 'signatures' for damage

"By comparing the DNA sequences, we found two mutational signatures for radiation damage that were independent of cancer type," said Campbell.

"We then checked the findings with prostate cancers that had or had not been exposed to radiation, and found the same two signatures again. 

"These mutational signatures help us explain how high-energy radiation damages DNA," Campbell said.

The study, published Monday in the journal Nature Communications, said the researchers had validated their findings in a published series of radiation-naive and radiation-exposed prostate tumours from 10 patients.

"This is the first time that scientists have been able to define the damage caused to DNA by ionizing radiation," said Adrienne Flanagan, a collaborating cancer researcher from University College London and Royal National Orthopaedic hospital.

Small number

She said these mutational signatures could be a diagnosis tool and help researchers determine whether some patients should be treated differently for certain cancers.

The researchers acknowledged that their study may be limited by the overall number of tumours that were examined and the small number of each tumour type.

They also said the relatively low number of mutations they directly linked to ionizing radiation may "seem surprising for such a well-known carcinogen."

"It is certainly considerably less than seen for cancers associated with exposure to tobacco, sunlight or aristolochic acid (a plant compound)," the study said.