Types of Breast Cancer

In order to understand breast cancer and how to treat it, it's important to understand how breasts work. Breasts are made up of lobules -- glands that produce milk -- and ducts which carry the milk from the lobule to the nipple (when milk is being produced). The ducts and lobules are surrounded by fatty breast tissue.

Breast cancer types

Breast cancer is a disease where cells grow and multiply abnormally. Breast cancer can form either in the lobules or in the ducts. A cancer that forms in the lobules is known as lobular carcinoma while a cancer that forms in the ducts is known as ductal carcinoma.

The ducts and lobules are connected like branches on a tree trunk, forming a closed system. The only openings out of the system are at the nipple. Thus, a breast cancer that is contained within this closed ductal system is said to be in-situ or non-invasive. A breast cancer that has spread outside of the ducts into the surrounding breast tissue is called invasive.

Breast cancer is further defined by whether it expresses the hormone receptors estrogen or progesterone. This is described as ER-positive and PR-positive. Tumors are also tested for a protein called HER2. Patients will receive specific treatments based on whether their tumors express ER, PR and HER2.

Lymph nodes and breast cancer

Each breast primarily drains into the lymph nodes under the arm (axillary lymph node chain), but occasionally they drain to the other chains of lymph nodes, for example lymph nodes on the side of the chest bone (internal mammary chain) and above the collarbone (supraclavicular chain).

Breast cancer cells can break off from the initial tumor and travel to other parts of the body through the lymph fluid (or the blood stream). Once in the lymph fluid, they pass through the lymph nodes and can get trapped. The presence of cancer cells in lymph nodes is an indication that the cancer has the ability to spread. For this reason, examining the lymph nodes may be an important step in determining breast cancer treatment.

Breast cancer staging

The stage of a breast cancer describes the extent of disease at the time of diagnosis. Breast cancer stage is determined by whether the cancer is non-invasive or invasive, the breast tumor size, whether cancer has spread to the lymph nodes, and whether cancer has spread to other parts of the body.

Stage 0 breast cancer is non-invasive, also called ductal carcinoma in situ (DCIS).

Invasive cancer ranges from stage I (earliest) to stage IV (most advanced).

When cancer has spread outside the breast and surrounding lymph nodes it is called metastatic, or stage IV. Metastatic breast cancer is most often found in the bones, liver, lung or lymph nodes outside the axilla, although it can occur in any organ. Even though it is growing in these organs, it is still considered breast cancer.