Scientists have called for a new drug to be developed, which can block a gene that multiplies the risk of breast cancer returning after treatment.
The POLQ gene increases the risk of breast cancer returning after treatment by eight times, researchers at the Cancer Research UK/MRC Gray Institute at Oxford University found, and a drug that could block this gene would increase cancer survival.
The scientists believe the gene may cause tumour cells to be more aggressive, and women who have cancers that are not sensitive to the hormone oestrogen - which accounts for around a quarter of women diagnosed with breast cancer every year - are at greater risk of having the gene impact their survival.
The results, published in the online journal Oncotarget on Thursday, show that out of 279 diagnosed with breast cancer in the early 1990s, those with POLQ gene activity had a dramatically increased risk of the cancer returning after treatment. Information from other studies in Holland and Sweden also confirmed the team's results.
Professor Gillies McKenna, Director of the University's Cancer Research Unit, said: "As POLQ is not switched on by most healthy tissues it is possible that if drugs could be developed to block this gene, they would make tumours more responsive to treatments such as radiotherapy and chemotherapy but not increase the side effects caused to healthy cells.
"Drugs that block POLQ may be able to reverse the very poor survival associated with over production of this gene."