Five common genetic variants have been identified that increase a woman's risk of developing breast cancer by up to 16%.
The discoveries take the total number of known common “low risk” genetic sites associated with breast cancer to 18.
As more mutations are found it increases the chances of combining them in a test for susceptibility to the disease.
Such a test could help doctors give advice to women at risk of breast cancer and assist with diagnosis and treatment.
Most of the variants appear to be associated with hormone-sensitive cancers which are stimulated by oestrogen. Most breast cancers are hormone sensitive.
To carry out the study, scientists scanned the genetic codes of more than 16,500 women with breast cancer and a family history of the disease, and around 12,000 women without breast cancer.
The findings were published in the journal Nature Genetics.
Professor Nazneen Rahman, from The Institute of Cancer Research in London, said: “Our results now take the total number of gene regions linked to the risk of breast cancer to 18, but we still don't know which genes are causing this increased risk.
“Identifying the underlying genes and mechanisms behind breast cancer development is essential to increasing our understanding of the disease and ultimately finding new treatments.”
Co-author Professor Doug Easton, director of Cancer Research UK's Genetic Epidemiology Unit at Cambridge University, said: “While each of these sites have a small impact on breast cancer risk, by finding more of these genes we may be able to develop a test that can predict more reliably a woman's risk of developing breast cancer.”
Breast cancer is the most common cancer in the UK with more than 45,500 new cases each year.
Lifestyle factors play an important role in influencing the risk of the disease, but inherited factors are also important.
Dr Helen George, head of science information at Cancer Research UK, which funded the study along with the Wellcome Trust charity, said: “This is by far the largest study of its kind to explore the common genetic variations that contribute to breast cancer risk.
“This research takes us a step closer to developing a powerful genetic test for the disease.”