Ductal carcinoma in situ, or DCIS, is a non-invasive breast cancer. It’s stage 0 breast cancer. With DCIS, the abnormal cells are contained in the milk ducts of the breast and have not invaded nearby tissue outside the milk ducts. It’s called in situ, which means in place and non-invasive because the abnormal cells haven’t left the milk ducts. When cancer cells spread from where they started into surrounding breast tissue, and possibly to nearby lymph nodes and other parts of the body, the cancer is called invasive. Most invasive breast cancer starts in the milk ducts and is referred to as invasive ductal carcinoma, infiltrating ductal carcinoma or IDC. It’s the most common type of breast cancer, making up 70% to 80% of all cases. For invasive ductal carcinoma:

• The prognosis depends on the stage and tumor grade,
• Tumor characteristics, such as hormone receptor status and HER2 status can vary, and
• Ductal carcinoma in situ, or DCIS, is often present.

Invasive breast cancer can also start in the lobules and is referred to as invasive lobular carcinoma, infiltrating lobular carcinoma or ILC. It’s the second most common type of breast cancer. ILC is often found in multiple sites of the breast and can be difficult to detect on a physical exam or mammogram because the cells often form a straight-line pattern instead of forming a lump. For invasive lobular carcinoma:

• The prognosis varies with the stage and tumor grade, but
• For any given stage or grade, it’s generally similar to that of IDC.
• ILC tumors are most often hormone receptor-positive and HER2-negative, and
• The pattern of metastasis may be slightly different from IDC. For example, ILC may metastasize to the gastrointestinal tract or the ovaries.

Metastasis occurs when breast cancer cells break away from the original tumor and spread beyond nearby lymph nodes to other organs of the body through the bloodstream or lymphatic system. This is called metastatic breast cancer or MBC. MBC is invasive breast cancer. It’s not a specific type of breast cancer; it’s the most advanced stage of breast cancer. The most common places the cancer spreads are the bones, lungs, liver or brain. For more information on non-invasive and invasive breast cancers, visit the Diagnosis section on komen.org.