The first signs of cancer can appear years if not decades before diagnosis, scientists have discovered, raising hopes for new tests to detect the disease much earlier.
One of the biggest international studies into the causes of cancer has found genetic mutations which drive the disease begin to occur long before any other signs begin to surface.
Researchers believe their findings could open the doors to quicker and more effective methods of cancer diagnosis and treatment.
Clemency Jolly of the Francis Crick Institute, one of the researchers involved in the research, said: "What's extraordinary is how some of the genetic changes appear to have occurred many years before diagnosis, long before any other signs a cancer may develop, and perhaps even in apparently normal tissue."
Dr Lincoln Stein of the Ontario Institute for Cancer Research in Canada, who was also involved in the research, said: "With the knowledge we have gained about the origins and evolution of tumours, we can develop new tools and therapies to detect cancer earlier, develop more targeted therapies and treat patients more successfully."
Around 40,000 new cancer cases are reported in Ireland every year, according to the Irish Cancer Society, with the disease causing more than 9,000 deaths annually - one in four of all deaths.
An international team of researchers looked at the genetic material, or genome, of tumours.
Their work, as part of the global Pan-Cancer Analysis of Whole Genomes project, involved creating the most comprehensive map on whole cancer genomes to date.
The team analysed and sequenced nearly 2,700 whole genomes of cancer samples and mapped mutations in 38 different types of tumours.
While human cells undergo billions of mutations, only a small number, called driver mutations, lead to cancer.
The researchers looked at how many times a single change, or driver mutation, had been replicated and copied across chromosomes.
Using what they describe as a "carbon-dating method", they were able to determine the order in which the mutations happened and the relative timing between them.
The team found these mutations occurred "particularly early" in ovarian cancer as well as two types of brain tumours.
Dr Peter Van Loo of the Francis Crick Institute and one of the researchers involved in the Pan-Cancer project, said: "We've developed the first timelines of genetic mutations across the spectrum of cancer types.
"For more than 30 cancers, we now know what specific genetic changes are likely to happen, and when these are likely to take place.
"Unlocking these patterns means it should now be possible to develop new diagnostic tests that pick up signs of cancer much earlier."
The comprehensive analysis is detailed in six papers published in 'Nature' and is as part of a wider collection of 22 papers published in other Nature Research journals.