CHICAGO: Mutations in the BRCA1 breast cancer gene appear to be linked with the loss of a protein important for putting the brakes on cell growth, a finding that could lead to new therapies, researchers said on Sunday.

The breakthrough could lead to more effective therapies for women with an aggressive and especially deadly cancer known as triple-negative that does not respond to current advanced drugs, the researchers said.

"It doesn't have a good target for therapy at this point," said Dr Ramon Parsons of Columbia University Medical Center in New York, who worked on the study. Scientists have known for more than a decade that women with certain alterations in the BRCA1 gene were at high risk for breast cancer. What they have not understood is exactly how a mutation in this gene leads to cancer.

Researchers at Columbia, working with at team at Sweden's Lund University, now believe mutations in the BRCA1 gene can leave cells incapable of repairing routine DNA damage. When such damage occurs in a protein called PTEN, which regulates the growth of cells, cell growth is unchecked and tumors form.

Women with faulty copies of BRCA1 or BRCA2 have a 50 to 85% chance of getting breast cancer. Mutations in these genes account for 5 to 10% of breast cancer cases. Most breast tumors are called estrogen-receptor positive, because they are fuelled by the hormone estrogen.