Cancer is a genetically driven disease, and a mother lode of new genetic data on dozens of different cancers is promising to break open fresh avenues of prevention and treatment. Nineteen out of 20 cancers now can be tracked back to one or more specific genetic mutations, based on data gathered from in-depth sequencing of thousands of whole-cancer genomes, researchers say.

"We can now identify in more than 95% of patients at least one genetic change that's biologically responsible for the tumor, and in many patients five to 10 or more of these causal mutations, which we call driver mutations," said project co-chair Peter Campbell. He's head of cancer, ageing and somatic mutation at the Wellcome Sanger Institute in England.

On average, cancer genomes contain four to five driver mutations, researchers report.

This knowledge will help researchers and doctors develop and choose from precise treatments targeting the specific mutations that are causing cancer in individual patients, Campbell said.

These findings take us "one step further down the road of understanding all the complexities of cancer," said Dr. William Cance, chief medical and scientific officer for the American Cancer Society.

Prior to this research, doctors were able to detect one or more genetic drivers of cancer in only about two-thirds of patients, Campbell said.

That's because previous genetic research into cancer focused solely on the exome -- the portion of a person's DNA that encodes proteins, said Dr. Lincoln Stein, head of adaptive oncology at the Ontario Institute for Cancer Research in Toronto.

"That's a mere 1% of the whole genome," said Stein, a member of the project. "Assembling an accurate portrait of the cancer genome using just the exome data is like trying to put together a 1,000-piece jigsaw puzzle when you're missing 99% of the pieces, and there's no puzzle box with a completed picture to guide you."

It all comes down to how different each person's cancer genetics are compared to other patients', and how those genetics have been influenced by events over a lifetime, Campbell said. Mutations come into play, as well as factors like smoking, sun exposure or obesity.

"We see thousands of different combinations of mutations that can cause the cancer, and more than 80 different underlying processes generating the mutations in a cancer," Campbell said. "Some of these processes reflect the wear and tear of ageing. Some reflect inherited causes. Some reflect the lifestyles that people have engaged in. All of these shape and mould the genome during cancer development."

By building on this base of genetic data, researchers hope that one day a doctor will be able to feed a patient's cancer genetics and lifestyle factors into a computer and come up with precise cures for their disease.

"The difficulty with preventing and treating cancer is that there are so many pathways that are involved in its creation," Cance said. "I think of cancer as a Darwinian phenomenon, where the cells can constantly change and survive."

But these researchers found that while mutations contribute to cancer in a multitude of ways, there are still about the same number of genes that cause cancer and ways that people develop it.

 HealthDay