Breast cancer genes can be hereditary

A deadly gene's path can hide in a family tree when a woman has few aunts and older sisters, making it appear that her breast cancer struck out of nowhere when it really came from Dad.


A new study suggests thousands of young women with breast cancer - an estimated 8,000 a year in the U.S. - aren't offered testing to identify faulty genes and clarify their medical decisions.


Guidelines used by insurance companies to decide coverage for genetic testing should change to reflect the findings, said study co-author Dr. Jeffrey Weitzel of City of Hope Cancer Center in Duarte, Calif. Testing can cost more than $3,000.


"Interestingly, it's about Dad," Weitzel said. Half of genetic breast cancers are inherited from a woman's father, not her mother. But unless Dad has female relatives with breast cancer, the faulty gene may have been passed down silently, without causing cancer.

Weitzel said doctors often overlook the genetic risk from the father's side of the family.


The study, appearing in Wednesday's Journal of the American Medical Association, looked at the genetic test results from 306 women diagnosed with breast cancer before age 50.


None of the cancer patients in the study had a family history of breast or ovarian cancer.


Among the women with plenty of female relatives, about 5 percent had BRCA gene mutations. But among those with few sisters and aunts older than 45 (when breast cancer would be likely to appear), almost 14 percent had mutations of the genes BRCA1 or BRCA2. That suggests that these cancer patients were unaware of their genetic mutations because there were so few women in the family to signal a cancer risk.


The researchers defined few female relatives as fewer than two on either the father's or mother's side of the family
Women who were adopted and don't know their family medical history should be aware of the findings, Weitzel said. Women whose female relatives died young before breast cancer had time to show up also are affected.


When such a woman gets breast cancer before age 50, she should get a genetic test, said Dr. Noah Kauff, a cancer geneticist at Memorial Sloan-Kettering Cancer Center in New York. That would help her decide whether to have the unaffected breast or her ovaries removed to prevent more cancer. Kauff was not involved in the research, but wrote an accompanying editorial.