Those clues center on the BRCA1 and BRCA2 gene mutations, which make breast cancer and ovarian cancer more likely.
In a new study, nearly 1,400 women diagnosed with breast cancer before age 55 got BRCA1 and BRCA2 genetic tests. They were also asked if their mother, daughters, or sisters had ever been diagnosed with breast cancer.
The vast majority of the breast cancer patients had no BRCA1 or BRCA2 gene mutations.
But 5% of the patients who had had breast cancer in one breast and 15% of those who had had breast cancer in both breasts had BRCA1 or BRCA2 gene mutations. Their close female relatives were more likely to have had breast cancer than the relatives of patients without BRCA1 or BRCA2 gene mutations.
Age also mattered. Younger breast cancer patients were more likely to have a mother, daughter, or sister with a history of breast cancer.
Besides BRCA1 and BRCA2, other genes likely "play a major role" in the study's breast cancer risk variation, and environmental and lifestyle factors may also have been involved, write the researchers.
They included Colin Begg, PhD, of New York's Memorial Sloan-Kettering Cancer Center. Their study appears in the Jan. 9/16 issue of The Journal of the American Medical Association.