Australian scientists revealed on Tuesday they had found that gene variants known to increase a woman's risk of breast cancer also played a determining role in the density of her breast.
Professor John Hopper, of the University of Melbourne's School of Population Health, said the discovery points to new "pathways" for the development of breast cancer, and it opens a new avenue for research into targeted treatment.
"Previous twin studies have suggested there is a genetic link between mammographic density and breast cancer," he said.
"For the first time, we have been able to identify some of the breast cancer genetic variants involved."
The research took in mammogram results and blood samples collected from 830 sets of twins and 600 of their sisters recruited via the Australian Twin Registry.
Scientists then looked for any link between women who had lots of "light areas" - high-density breast tissue - on their mammogram scans and a range of 12 gene variations known to increase the breast cancer risk.
"We aimed to determine if these genetic variants associated with breast cancer risk also influenced mammographic density ... and we found at least two of the variants were linked," said Dr Jennifer Stone, who led the research into mammographic density.
"This is the beginning of a new research focus on how cancers begin and the role mammographic density plays." (Xin Hua)