Nine new genes involved in the development of breast cancer have been uncovered, bringing the total number to at least 40.

Scientists led by a team at the Wellcome Trust Sanger Institute examined genetic changes in the breast tumours of 100 women.

The authors say their research, published in the journal Nature, gives a "sobering perspective on the complexity and diversity" of breast cancer, as no two breast cancers shared the same combination of faulty cancer genes.

Many cancers develop when non-inherited faults in genes accumulate during a person's lifetime.

Some faults are relatively harmless, but, so-called 'driver' mutations occur in cancer genes and contribute to the development of cancer.

Dr Patrick Tarpey from the Wellcome Trust Sanger Institute said: "To identify new cancer genes that lead to the development of breast cancer, we searched for driver mutations in over 21,000 genes, and found evidence for nine new cancer genes involved in the development of this cancer."

Most individual cancers contained different combinations of mutated genes.

The Institute's director, Professor Mike Stratton, said: "We found that breast cancer can be caused by more than 70 different combinations of mutations.

"If we consider three breast cancers, each with four driver mutations: they might share none of those driver mutations - so each is a different genetic 'animal'. They are different cancers driven by different genes. We need to classify them as carefully as we can. This study is a step towards that goal," he added.

Breast cancer is the most common cancer among women in the UK, with more than 48,000 women diagnosed with the disease every year.

The researchers hope that understanding genetic diversity in breast cancer will be an important step towards more rational treatment for the disease.

Professor Andy Futreal, also from the Wellcome Trust Sanger Institute, said: "One of the most striking things about breast cancer is how it progresses differently in each patient and how each patient responds differently to therapy. Our results can help us to understand these differences.

Professor Stratton added: "The picture is certainly more complicated than we would have wanted, but as with many other things knowledge is our strongest weapon.

Henry Scowcroft, science communication manager at Cancer Research UK, welcomed the research.

"This is a very important and rigorous analysis," he said.

"When taken together with other recent results, these new genes contribute to a detailed and ever-more complex catalogue of the genetic faults in breast cancer.

"And this knowledge will doubtless drive further research that will, when replicated in larger numbers of cancer samples, lead to better ways to diagnose and treat breast cancer patients in the future."

Source: CRUK