It's not clear what causes DCIS. DCIS forms when genetic mutations occur in the DNA of breast duct cells. The genetic mutations cause the cells to appear abnormal, but the cells don't yet have the ability to break out of the breast duct.

Researchers don't know exactly what triggers the abnormal cell growth that leads to DCIS. It's likely that a number of factors may play a part, including genes passed to you from your parents, your environment and your lifestyle.

Jun. 23, 2011