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Breast cancer is classified according to whether it has spread beyond the cells that line the thin tubes that carry the milk to the nipple (the ducts).

Doctors may also classify breast cancer based on how the cancer cells grow and the size and shape of the cancer cells. For example, a type of invasive breast cancer called medullary cancer has large cells. Also, the cells around the edges of the tumor look like cells from the immune system.¹

Non-invasive breast cancer is contained within the ducts of the breast. This means it hasn't spread beyond the lining of the ducts, or into the surrounding fat or other breast tissue. This type of cancer is also called in situ. (This means that it has stayed in the spot where it started growing and hasn't spread further.)

Some doctors divide non-invasive cancers into one of the following categories.

• Lobular carcinoma in situ: This is not actually cancer. It means that you have abnormal cells in the lobules of your breast. And you have an increased risk of getting breast cancer in the future.
• Ductal carcinoma in situ: This is cancer that started in the thin tubes that carry milk through the breast to the nipple (the ducts).

Because these cancers are so small that you can't feel them, they are usually found by chance during a mammogram. On a mammogram they look like little white specks. These specks are actually tiny spots of calcium.²

Invasive breast cancer has broken through the walls of the ducts and spread into the fatty tissue in the breast. From there it can get into the lymph vessels or blood vessels. It can then spread to other parts of your body.

Invasive breast cancer is classified according to how far it has spread. It may be called:

• Early breast cancer. This means that the cancer seems to be only in your breast or also in some of the lymph nodes under your arm. This type of cancer can be removed by surgery. It's also called operable breast cancer. It's possible that some cancer cells may have spread outside the breast or armpit area but can't be detected
• Locally advanced breast cancer. This means the cancer is bigger than 5 centimeters (around 2 inches), or has spread to your skin or to the front of your chest, or to both your skin and chest. The lymph nodes under your armpit might also have become matted together by the tumor.
• Metastatic (or advanced) breast cancer. This means that the cancer has spread through the blood vessels or lymph vessels to other parts of your body, such as your bones, liver or lungs
• Inflammatory breast cancer. This is a rare, invasive cancer that can block the lymph vessels in the skin over your breast. If you have this kind of breast cancer, your skin looks bumpy, like orange peel. Your skin may also feel warm and look red.

Most women with invasive cancer have early breast cancer that hasn't spread beyond the breast or nearby lymph nodes.

Invasive cancer is also called infiltrating breast cancer.

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment. ©BMJ Publishing Group Limited 2008. All rights reserved.