The researchers anticipate that these new insights into the workings of the disease will aid development of more targeted screening and prevention programs.
'Our study is another step towards untangling the breast cancer puzzle,' said Professor Doug Easton from the University of Cambridge, a lead author on the study. 'As well as giving us more information about how and why a higher breast cancer risk can be inherited, the genetic markers we found can help us to target screening and cancer prevention measures at those women who need them the most.'
In the study, published in Nature Genetics, the researchers analysed the genomes of over 120,000 women of European ancestry with and without breast cancer. By comparing their DNA sequences, they were able to pinpoint fifteen new single nucleotide polymorphisms (SNPs) - small genetic changes - that conferred increased risk with statistical significance.
These genetic factors have subtle, but incremental effects on breast cancer risk. So, while each SNP has little effect alone, inheriting enough of them can lead to an accumulated effect on the risk of the disease. The researchers estimate that five percent of women have enough of these SNPs to double their risk of breast cancer, giving them a one in four odds of developing the disease.
'The next bit of solving the puzzle involves research to understand more about how genetic variations work to increase a woman's risk. And we're sure there are more of these variations still to be discovered,' said Professor Easton.
In this regard, the authors have found some candidates to follow-up on. One of the hotspots mapped to a DNA section close to SETBP1, a gene not previously linked to breast cancer. It codes for a protein that is involved in duplicating the DNA in a cell, suggesting that any missteps in its workings could contribute to cancer development.
Research also published this week, in Cancer, showed that postmenopausal women have a 14 percent higher odds of developing breast cancer if a first-degree relative has been diagnosed with prostate cancer. This increase in risk jumps to 78 percent if a woman has a history of both breast and prostate cancer in the family. Since the two cancers share several similarities, there are likely to be common genetic risk factors. But, the researchers say it may also be that shared environmental factors also play a part in increasing the risk of both diseases among family members.