Breast cancer tumours have 10 subtypes, a scientific discovery that offers a roadmap to finding more tailored treatments, researchers in British Columbia say.

Investigators from the BC Cancer Agency, Cancer Research UK's Cambridge Research Institute and Manitoba Institute of Cell Biology at the University of Manitoba analyzed 2,000 tumour samples from women to "build the genetic encyclopedia of breast cancer."

The subtypes of cancer were related to over-activity or under-activity of specific genes as well as aggressiveness of the disease.

"Our results will pave the way for doctors in the future to diagnose the type of breast cancer a woman has, the types of drugs that will work, and those that won't, in a much more precise way than is currently possible," Prof. Carlos Caldas, the study’s co-lead author at the Cambridge Research Institute, told reporters.

Until now, breast cancer was classified based on biomarkers such as estrogen receptors. Drugs such as tamoxifen and Herceptin are prescribed depending on if the tumour expresses certain proteins.

When patient survival was plotted on a graph, 70 per cent of patients with one subtype lived 15 years compared with 35 per cent for another subtype, said the study's co-lead author, Dr. Sam Aparicio of the BC Cancer Agency in Vancouver.

The underlying genetics offer important information on why these differences occur and could guide treatment decisions, Aparicio said.

The scientists were puzzled that 17 per cent of the tumours showed few or no mutations, which reflects how much more there is to understand in breast cancer biology.

By mapping the tumours, the researchers were able to spot new patterns and find relationships between genes and pathways that may be disrupted in cancer.

While the findings are unlikely to help women who currently have breast cancer, the team hopes it will provide a springboard to develop new treatments.

Half of the funding came from Canada and half from the UK, through the BC Cancer Foundation, Canadian Breast Cancer Foundation - BC/Yukon Region and Prairies/NWT Region, Michael Smith Foundation and Cancer Research UK.