Researchers have made what's being called a breakthrough discovery in the fight against breast cancer. It is expected to kill more than 40,000 women this year alone but that could change. Researchers say they have unravelled the mysteries of how breast cancer begins and what makes it spread.

Breast cancer tissue samples could hold clues for finding future treatments. Canadian researchers are a step closer to unlocking how breast cancer develops and spreads after breaking one tumor's genetic code and zeroing in on cell mutations.

"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. So we've done it for the first time now," Dr. Samuel Aparicio with the British Columbia Cancer Agency said.

The Canadian team mapped out all 3 billion letters in the DNA sequence of one breast cancer patient's tumor then compared it to cancer that spread in the patient nine years later. They saw exactly how the cancer evolved by identifying each cell mutation.

"We may be able to develop treatments that are targeted to those specific changes or those specirfic genes in a patient's cancer," Breast Surgeon Dr. Sharon Rosenbaum-Smith said.

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 so they hope to start decoding tumors on a more routine basis, creating a data base for all types of breast cancers.

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

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.