Breast cancer is one of the most common cancers among American women, second only to skin cancer. About seven percent of women with breast cancer are diagnosed before the age of 40. Breast cancer accounts for more than 40 percent of all cancer in women in this age group.

The female breast is made up of lobules (milk-producing glands), ducts (tiny tubes that carry the milk from the lobules to the nipple), and stroma (fatty tissue and connective tissue surrounding the ducts and lobules, blood vessels and lymphatic vessels).

Most breast cancers begin in the cells that line the ducts (ductal cancers). Some begin in the cells that line the lobules (lobular cancers), while a small number start in other tissues.

• Ductal carcinoma in situ (DCIS), the most common type of noninvasive breast cancer, is found inside the ducts but has not spread through the walls into the surrounding area.
• Lobular carcinoma in situ begins in the milk-producing glands but has not grown beyond the lobules. 

One way breast cancer can spread is through the lymph system, which has several parts. Lymph nodes are small, bean-shaped collections of immune system cells (cells that are important in fighting infections); the nodes are connected by lymphatic vessels, similar to small veins but they carry a clear fluid called lymph away from the breast. Lymph contains tissue fluid and waste products, as well as immune system cells. Breast cancer cells can enter lymphatic vessels and begin to grow in lymph nodes.

Most lymphatic vessels in the breast connect to lymph nodes under the arm (axillary nodes). Some lymphatic vessels connect to lymph nodes inside the chest (internal mammary nodes) and those either above or below the collarbone (supraclavicular or infraclavicular nodes).

It’s important to know whether the cancer cells have spread to lymph nodes because if they have, there is a higher chance that the cells also may have gotten into the bloodstream and spread (metastasized) to other parts of the body. The more lymph nodes that have breast cancer, the more likely it is that the cancer may be found in other organs as well.

Staging is the process of finding out how widespread a cancer is when diagnosed. It is based on whether the cancer is invasive or noninvasive, the size of the tumor, how many lymph nodes are infected and whether the cancer cells have spread to other parts of the body. To help determine the stage of your cancer, a doctor may order imaging tests such as a chest X-ray, mammograms of both breasts, bone scans, computed tomography (CT) scans, magnetic resonance imaging (MRI) and/or positron emission tomography (PET) scans.

The stages of breast cancer are as follows:

Stage 0: Carcinoma in situ, in which noninvasive ductal or lobule cancer cells have not spread to nearby breast tissue. 

Stage I: In this early stage of invasive breast cancer, the tumor is no more than 2 centimeters (three-quarters of an inch) across and cancer cells have not spread beyond the breast.

Stage II: In this stage, the tumor is:

• No more than 2 centimeters (three-quarters of an inch) across, but cancer cells have spread to lymph nodes under the arm
• Between 2 and 5 centimeters (three-quarters of an inch to 2 inches) and no cancer cells have spread to lymph nodes under the arm
• Between 2 and 5 centimeters (three-quarters of an inch to 2 inches), but cancer has spread to the lymph nodes under the arm
• Larger than 5 centimeters (2 inches) and no cells have spread to the lymph nodes under the arm

Stage III: In this stage, cancer is considered locally advanced. There are three types.

Stage IIIA involves one of the following: 

• The tumor is no more than 5 centimeters (2 inches) across; cancer cells have spread to underarm lymph nodes that are attached to each other or to other structures. Or the cancer may have spread to lymph nodes behind the breastbone. 
• The tumor is more than 5 centimeters across; cancer cells have spread to underarm lymph nodes that are either alone or attached to each other or to other structures. Or the cancer may have spread to lymph nodes behind the breastbone. 

Stage IIIB: In this stage, a tumor of any size has grown into the chest wall or the skin of the breast. It may be associated with swelling of the breast or with nodules (lumps) in the breast skin. It also: 

• May have spread to underarm lymph nodes that are attached to each other or other structures. Or the cancer may have spread to lymph nodes behind the breastbone. 
• Inflammatory breast cancer is a rare type of breast cancer. The breast looks red and swollen because cancer cells block the lymph vessels in the skin of the breast. When a doctor diagnoses inflammatory breast cancer, it is at least stage IIIB, but it could be more advanced. 

Stage IIIC: This stage involves a tumor of any size and one of the following: 

• The cancer has spread to the lymph nodes behind the breastbone and under the arm. 
• The cancer has spread to the lymph nodes above or below the collarbone. 

Breast cancer is a type of cancer that can run in families and immediate relatives of patients that have been diagnosed. A woman’s risk of developing breast and/or ovarian cancer is greatly increased if she inherits a harmful BRCA1 or BRCA2 mutation.

BRCA1 and BRCA2 are human genes that belong to a class of genes known as tumor suppressor genes. They help ensure the stability of the cell’s DNA and help prevent uncontrolled cell growth. A mutation, or change, in the DNA of these genes has been linked to hereditary breast and ovarian cancer.

Local therapy is intended to treat a tumor at the site without affecting the rest of the body. Surgery and radiation therapy are examples of local therapies.

Systemic therapy refers to drugs which can be given by mouth or directly into the bloodstream to reach cancer cells anywhere in the body. Chemotherapy, hormone therapy and targeted therapy are systemic therapies.

Adjuvant therapy is additional cancer treatment given after the primary treatment to lower the risk that cancer will come back. Examples: chemotherapy, radiation therapy, hormone therapy, targeted therapy and biological therapy.

Neoadjuvant therapy is treatment given as a first step to shrink a tumor before the main treatment is given (usually surgery). Examples: chemotherapy, radiation therapy and hormone therapy. 

Operations for local treatment include breast-conserving surgery, mastectomy and axillary (armpit) lymph node sampling and removal. Breast reconstruction is also an option that can be done during the main treatment or later on.

In breast-conserving surgery, only part of the affected breast is removed, depending on the size and location of the tumor. These types of surgeries are usually followed by radiation and/or chemotherapy. For most women with stage I or II breast cancer, this type of surgery (followed by radiation and/or chemotherapy) is usually recommended.

A lumpectomy removes only the actual breast lump or tumor and a surrounding area of normal tissue. In a partial (segmental) mastectomy, more tissue is removed. In a quandrantectomy, one-quarter of the breast is removed.

In a mastectomy, all of the breast tissue is removed and the breast is not saved. There are two types:

• Simple/total mastectomy

The surgeon removes the entire breast, including the nipple, but does not remove the underarm lymph nodes or muscle tissue beneath the breast.

• Modified radical mastectomy

The surgeon removes the entire breast and some of the axillary (underarm) lymph nodes. This is the most common surgery for women with breast cancer who are having the whole breast removed.

Following a mastectomy or some breast-conserving surgeries, a woman may want to consider having the breast rebuilt, which is called breast reconstruction. These procedures are done solely to rebuild the breast so that it is about the same size and shape as it was before; it is not part of the cancer treatment.

Decisions about the type of reconstruction and when it should be done depend on each woman's medical situation and personal preferences. You may have a choice between having your breast reconstructed at the same time as surgery (immediate reconstruction) or at a later time (delayed reconstruction).

There are several types of reconstructive surgery. Some use saline (salt water) or silicone implants, while others use tissues from other parts of your body (autologous tissue reconstruction). The nipple and areola (darker area around the nipple) also can be preserved and added.