Relatives of women with breast cancer are being told not to panic, with new research revealing their risk of developing the disease has been exaggerated.
Professor John Hopper from the Australian Breast Cancer Family Study released the study's findings in Sydney today.
The study - which excluded relatives of women with the high-risk breast cancer genes BRA1 and BRA2 - found the chance of developing the disease for relatives of those already diagnosed depended on what type of breast cancer they had.
"If you have a close relative with breast cancer we think you have a two to three times increased risk," Professor Hopper told AAP.
"But for one-third there is no increased risk, no genetic cause at all.
"We can say to a group of relatives, 'you're not at increased risk, don't panic'."
Professor Hopper said there were multiple causes of breast cancer - "multiple genes and pathways".
But new research also shows that one in six relatives' risk of developing breast cancer has been underestimated.
"That risk is not explained by what we know about genes today," Professor Hopper said.
Professor Hopper was speaking along with Westpac chief executive Gail Kelly and National Breast Cancer Foundation patron Sarah Murdoch at the launch of the next phase of recruitment for Register4, an online community for breast cancer research volunteers.
The NBCF is calling for more families to volunteer for Register4 so that more high-risk genes might be discovered in the next phase of the research.