What causes dcis breast cancer?

In one word unknown : Ductal carcinoma in situ dcis is simply the sleeping cancer cells inside the breast ducts, like a garden hose loaded with cancer cells safe if they are inside the duct , once they are out side then is invasive cancer, ready to spread, cause is unknown at this time, from genetic mutations, braca i & ii age, hormonal uses.Environment , late age pregnancy life style etc are all attributed.

Unknown: Probably has the same risk factors as any breast cancer. Having a family history of bc is one of the most common "risk factors", but any woman can develop dcis, just like all women are at some risk for developing breast cancer.