Canadian researchers announced Wednesday they have figured out the genetic makeup of the deadliest form of breast cancer, a breakthrough that may one day help doctors devise a treatment plan that better targets their patients' disease.

Scientists at the BC Cancer Agency said the genetic code for triple negative breast cancer shows that it is a complex type of tumour with a wide range of potential mutations.

The researchers liken the genetic sequence to a "mini ecosystem," and say its evolution may explain why currently available treatments can be ineffective against triple negative breast cancer.

They say their findings now make it possible for them to estimate how the disease's genetic mutations evolved prior to diagnosis.

Lead study author Dr. Sam Aparicio, a professor at the University of British Columbia and chair of breast cancer research at the BC Cancer Agency, said the results prove that triple negative breast cancer is not a "uniform subtype" of the disease.

"It's actually extremely complex, with each cancer at a different stage in the evolutionary process at the time of diagnosis, which helps to explain why patient responses to treatment differ greatly," Aparicio said in a statement.

"What's extremely motivating with these findings is the opportunity to design clinical trials for patients with triple negative breast cancer so we can explore patient responses to treatment at the genetic level and look at ways to improve therapies and outcomes for patients."

The study included researcher teams from the University of British Columbia, Cross Cancer Institute of Alberta and Cancer Research UK/University of Cambridge. Their findings were published Wednesday in the online edition of the journal Nature.

Triple negative breast cancer is so named for the three cancer-causing proteins that it's missing: the estrogen receptor, progesterone receptor and ERBB2 receptor. These tumours do not respond to drugs that target hormones, such as Tamoxifen or Femara, or to Herceptin, which targets the HER2 receptors.

Triple negative breast cancer is typically more aggressive than other types of breast cancer. It accounts for 16 per cent of all breast cancer cases, or about 3,800 cases in Canada, and about 25 per cent of breast cancer deaths.

It is often treated as a single disease, but the researchers say their findings prove that patients' tumours can encompass a vast array of genetic mutations. Understanding these mutations and the role they play in a tumour's growth is key to figuring out why patients respond differently to treatment, and important for the development of more effective treatments, they say.

The researchers say they found groups of mutations for which there are already potential treatments in about 20 per cent of the 104 cases they studied.