Scientists have found a region of DNA that can increase or decrease the high chance of breast cancer linked to a particular gene variant - a finding that could help doctors keep a closer eye on women most at risk.
The findings were published in Nature Genetics journal on Sunday along with two other separate studies linking this same region and four others to ovarian cancer.
The breast cancer study centered on women who carry a faulty BRCA1 gene, which significantly raises the risk of developing certain cancers. On average, around 65 percent of women carrying a faulty BRCA1 gene will develop breast cancer, and around 40 percent will develop ovarian cancer, by the age of 70.
The studies found that if a woman with a BRCA1 fault also carries a "risk version" of a DNA region known as 19p13, her breast cancer risk may be even higher still.
"We've found a DNA region that acts like a volume control - to turn up or down the risk of developing breast cancer from faults in the BRCA1 gene," said Antonis Antoniou of Cambridge University, who led the work on the first study.
"Our discovery is the first step in a much larger study to identify genetic factors that modify breast cancer risk in women carrying BRCA1 mutations, and ultimately could help us assess the risk for each woman and monitor for the disease."
Breast cancer is the most common cancer among women, with more than a million new cases diagnosed worldwide each year.
In a separate study, the same 19p13 region was also shown to increase the risk, to a lesser degree, of ovarian cancer in women who are not carriers of a BRCA1 fault.
"This is important because it suggests that women who carry certain versions of this DNA stretch could benefit from closer monitoring for both breast and ovarian cancers," said Simon Gayther at University College London, who led that study.
A third study conducting by scientists from Europe, the United States, Canada and Australia found four other separate genetic regions also associated with ovarian cancer risk in the general population.
Ovarian cancer is the fifth most common cancer among women in developed countries. An estimated 230,000 women worldwide are diagnosed it each year and it kills around 130,000 each year.
Most women are not diagnosed until after the cancer has spread, because its symptoms are hard to detect, and nearly 70 percent of those with advanced disease die within five years.
"These latest findings raise the possibility that in the future, women...who are at the greatest risk of developing ovarian cancer because they carry these newly discovered DNA variants can be identified and given closer surveillance to look for early signs of ovarian cancer when it is most treatable," said Andrew Berchuck, a professor of gynaecologic oncology at Duke University Medical Center, who worked on the study.
"It also suggests that preventive approaches could be targeted toward these women."