The findings could help to provide insight into how breast cancer develops and have the potential to be used in genetic screening tools to more accurately identify women with a higher risk of developing the disease.
The study found that two genetic variants — rs10816625 and rs13294895 — were associated with a 12 percent and nine percent greater risk of breast cancer, respectively. The increased risk was moderately higher for oestrogen-receptor positive breast cancer, the most common form of breast cancer — at 14 percent for rs10816625 and 11 percent for rs13294895.
The study, led by researchers at the Institute of Cancer Research in London, used a technique called fine mapping analysis to focus on a specific region of chromosome 9 that had previously been identified as a 'hotspot' for breast cancer genetic risk. Researchers were looking for one letter differences in the DNA code — called SNP (single nucleotide polymorphism) — that were present more often in women with breast cancer than in women without the disease.
The researchers investigated the two new genetic variants further and found that they affect the activity of a gene called KLF4, which is involved in controlling how cells grow and divide.
Dr Nick Orr, team leader in Complex Trait Genetics at the Institute of Cancer Research, who led the study, said: 'Our study zoomed in on an area of our genome that we knew was linked to breast cancer risk, and has identified two new genetic variants that add significantly to our knowledge about the genetic causes of the disease.'
'The more genetic risk factors for breast cancer we discover, of which there are currently more than 80, the more accurately we will be able to predict who is at risk of getting the disease. Ultimately this will be vital for designing preventative strategies against breast cancer.'
The DNA of 86,000 women of European ancestry, 12,000 women of Asian ancestry and 2,000 women of African ancestry were analysed in the study, which was published in the journal Human Molecular Genetics.
The study involved a collaboration between more than 130 research institutions around the world, including the London School of Hygiene and Tropical Medicine, and the University of Cambridge. It was funded by a range of organisations including Cancer Research UK, Breakthrough Breast Cancer, and the European Union.
Dr Emma Smith, senior science information officer at Cancer Research UK, said: 'Thanks to modern technology we're building an increasingly detailed picture of the small variations in DNA that can influence a woman's risk of breast cancer.'
'The next challenges are understanding the biology underpinning their effects, so we can use this information to predict individual risk more accurately, improve screening and find better ways to treat and prevent breast cancer.'