What is the difference between DCIS and invasive breast cancer?

The primary difference between Ductal Carcinoma In Situ (DCIS) and invasive breast cancer lies in whether or not the cancer cells have spread beyond the milk duct.

DCIS (Ductal Carcinoma In Situ)

• Location: The abnormal cells are found only inside the lining of a milk duct.
• "In Situ": This means "in its original place." The cells have not spread into the surrounding breast tissue.
• Nature: It is considered non-invasive or pre-invasive. Because it has not spread, it cannot metastasize (travel to other parts of the body) in its current form. However, it is treated because, if left alone, it has the potential to develop into invasive cancer in some cases.

Invasive Breast Cancer

• Location: The cancer cells have broken through the wall of the milk duct and have begun to invade the surrounding breast tissue.
• Nature: Because these cells have moved into the surrounding tissue, they have access to blood vessels and lymph nodes. This gives them the potential to spread (metastasize) to other areas of the body.
• Classification: This is what is typically referred to when people talk about a "breast cancer diagnosis" that requires more systemic treatment (such as chemotherapy or hormone therapy) to address the risk of spread.

In short, DCIS is contained within the duct, while invasive breast cancer has breached the duct and moved into the surrounding tissue. If you or a loved one are navigating a diagnosis, your medical team will provide specific details on the grade of the cells and the recommended treatment path.