Does dcis usually turn into invasive breast cancer?

No: It is estimated that approximately 10-50% of all cases of dcis if left untreated would progress to invasive cancer. While some subtypes are more aggresive than others, it is hard to predict which are more likely to become invasive; therefore, our treatment of dcis is geared towards erring on the side of caution and treating all cases as if they could become invasive if left untreated.

In time: Dcis means cancer cells are inside the ducts and have not invaded. In time these cells will cross the duct wall and invade the breast tissues resulting in invasive cancer. Sometimes dcis can enlarge and remain in one lesion and not invade. Sometime even up to several centimeters. So it does not always lead to invasion. That's why we remove dcis before it does this. But if left alone it would.

If left alone: Current thought is that if left untreated, dcis will develop into invasive breast cancer.