Dr. Tom Hudson says scientists can now see how tobacco constantly alters DNA. (CBC)

Researchers have mapped the DNA mutations in skin and lung cancer — findings that one researcher says will change how cancer is viewed.

For lung cancer, the British team found almost 23,000 mutations — one mutation for every 15 cigarettes smoked.

"This is a fundamental moment in cancer research," said Prof. Michael Stratton from the Wellcome Trust Sanger Institute in Cambridge. "From here on in we will think about cancers in a very different way."

Scientists knew that smoking causes genetic mutations than can start tumours. But they didn't expect to see evidence of the genome bearing scars of every cigarette smoked. When they catalogued the mutations, they saw how cancer-causing agents in tobacco repeatedly bombard the DNA.

As with lung cancer, the second paper on melanoma showed repeated evidence of damage to DNA, this time from exposure to ultraviolet light. The team found about 33,000 mutations related to melanoma.

"Let's decrease exposure, let's stop smoking, use sun protection and so on, and actually we will be decreasing the chances of having cancer," said Dr. Tom Hudson of the International Cancer Genome Consortium in Toronto. "Prevention is probably the most important message to be had."

The genetic sequences that were studied came from tumours from two men who died from their diseases. The researchers compared normal and cancerous cells from the patients to find the genetic changes behind their fatal cancers.

Prospect of new tests, drugs

Now the time-consuming challenge is to learn more about these deadly mutations, and translate this knowledge into something that is clinically useful, Hudson said. In the meantime, there's no point in people calling to ask for their cancer genome, he said, because researchers wouldn't yet know how to use the information.

The international team of scientists from the U.S., Australia, Canada, China, France, India, Japan and Singapore will now sequence several hundred more tumours from different patients to look for key mutations that could become targets for future drugs. It's the biggest genetic sequencing effort since the human genome project first gave scientists a look at the blueprint of life.

There are tens of thousands of mutations in cancer DNA, but researchers say it's likely that only a handful of those mutations are responsible for making a cell cancerous.

Every year, 20,000 Canadians develop lung cancer, but by the time symptoms emerge it's usually too late to treat, which is why 95 per cent of patients don't survive. Worldwide, lung cancer kills around one million people each year.

Melanoma kills more than 900 Canadians a year, according to Canadian Cancer Society statistics.

With files from the Australian Broadcasting Corporation