Douglas Easton from Britain's University of Cambridge led the largest genome-wide analysis of breast cancer patients to date, scanning the gene maps of 16,536 patients, and found five new common gene variations.
The findings add to 13 other common genetic variants for breast cancer and will help explain around 8 percent of the risk of getting the disease, Easton and colleagues wrote in a study published in the journal Nature Genetics on Sunday.
A few, high-risk gene variants that occur much more rarely account for another 20 percent of breast cancer risk.
Breast cancer is the most common type of cancer in women in rich nations. It kills around half a million people worldwide each year.
Family history is a well-established risk factor. Having a close relative with breast cancer approximately doubles a woman's risk for the disease.