A UK research team has taken an important step forward in improving our understanding of the origins of breast cancer.

Scientists at the Breakthrough Breast Cancer Research Centre at The Institute of Cancer Research (ICR) in London have found evidence suggesting that aggressive forms of breast cancer are likely to develop from intermediary - slightly more developed - cells, rather than from stem cells.

If this proves to be the case, it will help scientists focus on the best new avenues of research to prevent and treat cancer.

Publishing their work in the journal Cell Stem Cell, the researchers introduced faulty BRCA genes - which are linked to inherited forms of breast cancer - into the stem cells in some mice, and into the intermediary cells of other mice.

They found that cancers which developed from stem cells did not resemble inherited breast cancer.

In contrast, cancers that formed from intermediary cells were strikingly similar to certain aggressive types of breast cancer such as inherited forms of the disease.

Contrary to what was previously thought to be most likely, this suggests that these types of breast cancer form in intermediary cells rather than stem cells.

Study leader Dr Matt Smalley, whose findings are published in the journal Cell Stem Cell, commented: "These results represent a major advance in our understanding of breast cancer. It means we can now look very closely at where the disease forms and which genes are involved in that process. This knowledge will greatly improve the chance of finding effective new targeted treatments for breast cancer patients in the future."

Professor Alan Ashworth, director of the Breakthrough Breast Cancer Research Centre, added: "Understanding the biology of breast cancer is essential for the future development of new ways to treat and prevent the disease. Our research gives a considerable new insight into how the disease forms and grows."

Dr Laura Bell, Cancer Research UK's science communications officer, said: "This new research gives us important clues about how aggressive breast cancers start, and could open new avenues of research for preventing and treating the disease."