What Causes Breast Cancer?

BRCA gene.

Random changes or mutations in the body’s DNA -- the genetic instructions found in cells that all people are born with -- is what causes breast cancer to occur. These changes in DNA can be inherited, meaning they are passed down from one generation to another, or acquired, meaning that there is a change in the DNA of one breast cell for reasons that are unclear and unknown.

Inherited Gene Mutations

Scientific research has revealed that certain inherited genes can increase the risk of developing breast cancer in some women. An inherited mutation of the BRCA1 and BRCA2 genes is the most common cause of inherited breast cancer. In women with this mutation, the risk of developing breast cancer can be as high as 80 percent.

Other inherited gene mutations such as ATM, p53, CHEK2, PTEN and CDH1 also can increase the risk of developing breast cancer. However, these gene mutations are more rare than the BRCA1 and BRCA2 genetic mutations.

Acquired Gene Mutations

While genetics does play a role in causing breast cancer, it is important to point out that less than 15 percent of all breast cancers occur in women with a family history with the disease. In fact, more than 85 percent of all breast cancers are caused by acquired gene mutations of an unknown cause.

One example of an acquired gene mutation is HER2 (human epidermal growth factor-2). Having too many copies of the HER2 gene is associated with a more aggressive, faster growing form of breast cancer. Approximately 20 to 25 percent of all breast cancers are HER2-positive.

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