Most cases of breast cancer are not caused by inherited genetic factors. These cancers are associated with somatic mutations in breast cells that are acquired during a person’s lifetime, and they do not cluster in families.
In hereditary breast cancer, the way that cancer risk is inherited depends on the gene involved. For example, mutations in the BRCA1 and BRCA2 genes are inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to increase a person’s chance of developing cancer. Although breast cancer is more common in women than in men, the mutated gene can be inherited from either the mother or the father.