The mutations that most often cause breast cancer are changes in the BRCA1 and BRCA2 genes ("Breast cancer 1 gene" and "Breast cancer 2 gene").
Women with inherited mutations in the BRCA1 or BRCA2 genes are three to seven times more likely to develop breast cancer than those who do not have the mutations, and at an earlier age. There are also many other less common gene mutations that can cause breast cancer (for example, PTEN, p53, CDH, ATM, CHEK2 among others).
According to the National Cancer Institute (NCI), the women who are mostly likely to have BRCA1 or BRCA2 mutations are those of Eastern European (Ashkenazi) Jewish heritage and/or those with family members who have had:
- Multiple cases of breast cancer
- Cases of both breast and ovarian cancer, or
- One or more family members with two primary cancers (original tumors at different sites)
However, the NCI also notes that not every woman in such families carries an alteration in BRCA1 or BRCA2, and not every cancer in such families is linked to alterations in these genes.