"This is the first time that we've been able to look at the entire set of genes from a cancer patient, and that is key because that's going to help us understand what goes wrong," said Dr. Richard Wilson of Washington University in St. Louis, the senior author on the study.
Using donated cells from a woman who died of leukemia, researchers compared the individual genes -- all 20,000 of them -- from her cancer cells, to those from her normal, healthy cells.
Using DNA sequencing, they were able to identify 10 genetic "mutations," or mistakes in the cancer cells that could have caused her cancer. Out of the 20,000 genes, 10 defective genes, which developed later in life, appeared to spiral out of control.
One of the newly discovered abnormal genes blocks chemotherapy drugs from ever getting inside the cancer cells to kill them.
Four others appear to turn off a cell's "early warning system" that would normally prevent a healthy cell from ever turning into a cancer cell.
"If those genes are mutated or de-activated, there's a very good chance the cancer can start to grow out of control," Wilson told ABC News.
The study, conducted at Washington University over many months, was published today in the medical journal Nature.
Advances Hold Promise for Cancer Treatment
Researchers are now trying to identify all the genetic mistakes that can cause lung, brain and ovarian cancers, with the hope of one day being able to identify each and every cancer patient's unique genetic make-up with a simple blood test.
These new genetic cancer "codes" will not only help develop more targeted drugs in the future, but they'll also improve how existing cancer medications are used today.
Doctors will likely be able to customize patients' care by consulting their genes and spot aggressive cases well in advance.
This research will help doctors when "... deciding which patients get which treatment, which patients need more treatment, which patients are more likely to have their cancer come back," said Dr. Ross Levine of Memorial Sloan-Kettering Cancer Center in New York City. "It's incredibly transformative in the clinical arena, right away."
While questions linger, like why these mutations occur in the first place, this research is unlocking long-held secrets, one cancer at a time.