And now, new treatments based on a discovery by experts at the Institute of Cancer Research could save thousands of women's lives in the future.
The scientists have made a major breakthrough by identifying an enzyme made in the body that they believe is responsible for the spread of breast cancer cells to other parts of the body.
The discovery is particularly significant because it's the spread of cancer to organs such as the lungs, bone and liver - a process called metastasis - that causes 90% of cancer deaths, the experts explain. And while these days cancer can often be successfully treated if it's diagnosed early enough, there's currently little hope of stopping it once it starts spreading in the later stages of the disease.
The enzyme, called lysyl oxidase-like 2 (LOXL2), promotes the spread of breast cancer through its control of two proteins called TIMP1 and MMP9 (the proteins are thought to help cancer cells to spread).
Many of the 12,000 women who die from breast cancer every year in this country lose their lives because their cancer has spread.
Writing in the journal Cancer Research, the scientists suggest the next step is to develop drugs that block LOXL2 - which is also thought to play a part in the spread of certain other types of cancer.