Scientists are closing in on more genes linked to the development and progression of breast cancer.
Gene faults affect tumour development
Several genes, which are either inherited or altered during a woman's lifetime, have already been identified.
Scientists have now pinpointed another fault which can develop - and have identified four genes which could be the culprit.
The study, in the journal Oncogene, found the fault in a quarter of breast tumours analysed.
Breast cancer is the most common cancer for women in the UK, with over 41,000 cases diagnosed each year.
A woman has a one in nine lifetime risk of developing breast cancer.
Inherited faulty genes such as BRCA1 and BRCA2 account for fewer than 1 in 20 breast cancer cases.
But most cases are caused by genetic mutations which occur in breast cells during a woman's lifetime.
Researchers have so far only pinpointed a few of the possible genes involved.
University of Cambridge researchers used technology called DNA microarrays, which can scrutinise the activity of hundreds of genes at once.
Previously, they would have had to analyse one gene at a time.
The team examined the tissue of 33 breast tumours and also breast cancer cells grown in the laboratory, focusing on chromosome 8 which had previously been identified as a possible place for cancer-related gene faults.
Using microarrays, they were able to narrow down which of the hundreds of genes were likely to be actively involved in tumour development.
Four candidate genes were identified on a specific area of chromosome 8.
People should have two copies of the whole chromosome.
But women with this genetic fault had multiple copies of this particular fragment containing the four potential culprit genes - FLJ14299, C8orf2, BRF2 and RAB11FIP.
This pattern was seen in eight out of the 33 tumours studied.
Professor Carlos Caldas, based at the Department of Oncology and the Hutchison/MRC Research Centre at the University of Cambridge, told the BBC News Website: "We don't know which of the four genes is the culprit yet.
"But we know that women who have increased copies of this fragment of chromosome eight have a poor prognosis.
"We could use this to identify tumours that are more aggressive and target them with more aggressive treatment."
Dr Lesley Walker, head of cancer information at Cancer Research UK, said: "DNA microarray technology holds much promise for the future, however, it's important to remember that this work wouldn't have been possible without the patients who gave informed consent for their tumours to be used for research.
"Without them, science couldn't progress at the pace it does and the treatments many of us are likely to be personally grateful for in our lifetimes would probably be delayed by generations."