Scientists still do not fully understand the causes of breast cancer. Research has shown that certain risk factors increase the likelihood of developing breast cancer. And while gene mutations can cause healthy breast cells to become cancerous, many of those gene changes have not yet been pinpointed by researchers.

Genes influence how cells work. The proto-oncogenes contained by normal cells regulate cell growth, and genes called tumor-suppressor genes, which determine how often cells divide. If proto-oncogenes or tumor suppressor genes mutate, cells can become cancerous.5

Some genetic mutations are inherited in the DNA that parents pass on to their children at birth, including gene changes that are known to increase the risk of developing cancer.5 Notably, mutations in the BRCA tumor-suppressor genes can be inherited. Yet only around 10% of breast cancer diagnoses are linked to known inherited gene abnormalities. Other cases may develop from still-unknown hereditary mutations. About 90% of breast cancers are thought to arise from unidentified acquired gene changes that happen after birth, stemming from factors like radiation, exposure to cancer-causing chemicals, or random cellular changes.5