Scientists hail a "landmark" breakthrough in the fight against breast cancer

It's being called a breakthrough discovery in the fight against breast cancer. Canadian researchers say they've unraveled the mysteries of how breast cancer begins and what makes it spread.

Canadian scientists have exposed exactly what's inside a breast cancer tumor. By figuring out all three billion letters in the tumor's DNA sequence, they've zeroed in on cell mutations, shedding light on how the disease develops and spreads.

"We've never had the possibility to go in and retrieve all of the sequence and all of the mutations present in any particular cancer," explained Dr. Samuel Aparacio of British Columbia's .

The study marks such an important turning point in the fight against cancer it's landed on this week's cover of the journal .

The Canadian team mapped the genetic makeup of a breast cancer patient's original tumor and compared it to the same patient's tumor that spread nine years later. They saw exactly how the cancer evolved by identifying each cell mutation.

This year alone, more than 190,000 women in the U.S. are expected to get breast cancer. Doctors say this study could have huge implications for the development of new drugs and more personalized treatments.

"We still subject a lot of women to treatments of uncertain benefits," said medical oncologist Dr. Daniel Rayson. "Anything that helps us narrow the treatment focus down is going to be a major advance."

So far, researchers have only sequenced the genes in one patient's tumor. But new technology allowed them to do it in just a few weeks. They hope to start decoding tumors on a more routine basis, creating a database for all types of breast cancers.

"We're not quite there yet, but this is an important step forward," commented Aparacio.

Not only do scientists hope to tackle breast cancer in this way. They're also setting their sights on decoding the tumors of other cancers.