It's long been known that faulty BRCA genes greatly raise the risk for breast cancer. Now scientists say a more recently identified, less common gene can do the same.

Mutations in the PALB2 gene can make breast cancer up to nine times more likely to develop, an international team of researchers reported in this week's New England Journal of Medicine.

About 5 percent to 10 percent of breast cancers are thought to be caused by bad BRCA1 or BRCA2 genes. Beyond those, many other genes are thought to play a role, but how much each one raises risk has not been known, said Dr. Jeffrey Weitzel, a genetics expert at City of Hope Cancer Center in Duarte, Calif.

The new study on the PALB2 gene shows "this one is serious" and probably is one of the most dangerous in terms of breast-cancer risk, said Weitzel, one of leaders of the study.

The study involved 362 members of 154 families with PALB2 mutations -- the largest study of its kind. The faulty gene seems to give a woman a 14 percent chance of breast cancer by age 50 and a 35 percent chance by age 70, with the risk even greater if she has two or more close relatives with the disease.

That's nearly as high as the risk from a faulty BRCA2 gene, Dr. Michele Evans of the National Institute on Aging and Dr. Dan Longo of the medical journal staff wrote in a commentary in the journal.

The PALB2 gene works with BRCA2 as a tumor suppressor, so when it is mutated, cancer can flourish.

Researchers don't know how common the mutations are, but it's "probably more than we thought because people just weren't testing for it," Weitzel said. He said he has found three cases among his breast-cancer patients in the past month.

Among breast-cancer patients, BRCA mutations are carried by 5 percent of whites and 12 percent of eastern European (Ashkenazi) Jews. PALB2 mutations have been seen in up to 4 percent of families with a history of breast cancer.

Men with a faulty PALB2 gene also have a risk for breast cancer that is eight times greater than men in the general population.

PALB2 often is included in more comprehensive genetic testing, and the new study should give people with the mutation better information on their risk, Weitzel said. Doctors said that people with faulty cancer genes should be offered genetic counseling and may want to consider more frequent screening and prevention options, which can include hormone-blocking pills or breast removal.

Actress Angelina Jolie had her healthy breasts removed last year after learning she had a defective BRCA1 gene.

The study was funded by many government and cancer groups around the world and was led by Dr. Marc Tischkowitz of the University of Cambridge in England. The authors include Mary-Clare King, the University of Washington scientist who discovered the first breast cancer predisposition gene, BRCA1.

A Section on 08/07/2014