Stage zero is non-invasive breast cancer, or ductal carcinoma in situ, sometimes called DCIS.

With DCIS, the abnormal cells are contained in the milk ducts. It’s called “in situ” (which means “in place”) because the abnormal cells have not left the milk ducts to invade nearby breast tissue.

Depending on how far the DCIS has spread within the milk ducts, surgery can be mastectomy or lumpectomy.

In general, women treated with mastectomy for DCIS don’t benefit from radiation therapy.

Lumpectomy for DCIS is usually followed by whole breast radiation therapy to lower the risk of DCIS recurrence and invasive breast cancer in the treated breast.

Hormone therapy isn’t recommended for women who have a mastectomy for DCIS.

Women who are treated with lumpectomy for estrogen receptor-positive DCIS should consider taking hormone therapy (either tamoxifen or an aromatase inhibitor) for 5 years to lower the risk of DCIS recurrence and invasive breast cancer (in both breasts).

Chemotherapy and other breast cancer drug therapies are not used to treat DCIS.