One of the first places breast cancer can spread and grow is in nearby lymph nodes, which are part of the body’s lymphatic (lymph) system. The lymphatic system plays an important role in the body’s immune system, which protects you against infection and disease, and is made up of three parts:

1. Lymph, a clear fluid that circulates through the lymphatic system
2. Lymphatic vessels
3. Lymph nodes

The lymph system’s primary function is to circulate the lymph, which contains infection-fighting white blood cells, throughout the body and to flush your body of toxins, waste, and other unwanted materials.

As breast cancer cells multiply, they can enter the lymphatic vessels that are located in a woman’s breast tissue. The lymph fluid then carries the cells throughout the body. Often times, the lymph nodes in the underarm area are the first place breast cancer will start to grow since they are the closest to the breast.

The tests used by the oncologist to determine that there are breast cancer cells in the lymph nodes is called lymph node evaluation.

Determining Lymph Node Involvement

Your breast cancer specialist will remove one or several underarm lymph nodes so they can be biopsied and then examined under a microscope to determine if lymph nodes are involved.

There are two different ways lymph nodes can be checked. The most common and least-invasive method is called sentinel lymph node biopsy. The other is called axillary lymph node dissection.

In most cases, lymph node surgery is done as part of the main surgery to remove the breast cancer. There are times, however, when it may be done as a separate operation.

Sentinel Lymph Node Biopsy (SLNB)

A sentinel lymph node is defined as the first lymph node to which cancer cells are most likely to spread from a primary tumor. There are times more than one sentinel lymph node is present.

During surgery to remove early-stage breast cancer, the sentinel node is identified and then removed so it can be sent to a pathologist (a physician who studies the causes and effects of diseases). The pathologist will determine if there is cancer in it. This procedure to remove the sentinel lymph node so it can be examined is called a sentinel lymph node biopsy (SLNB).

To identify the sentinel node the surgeon will:

• Inject a radioactive substance, a blue dye, or both near the tumor
• Use a device that detects radioactivity to find the sentinel node or looks for lymph nodes that are stained with the blue dye
• Make a small incision (about 1/2 inch) in the overlying skin and remove the node once it has been located

The results of the pathology exam help determine breast cancer stage and help plan treatment.

If no cancer is found in the sentinel nodes (lymph node-negative), surgery to remove more lymph nodes will not be needed because it is unlikely other lymph nodes have cancer. If cancer is found in the sentinel nodes (lymph node-positive), more lymph nodes may be removed with a procedure called axillary dissection. However, in select low-risk cases with pre-specified criteria and only 1 to 2 lymph nodes involved, lymph node axillary dissection can be avoided in cases of breast preservation where radiation therapy is part of the planned management.

Axillary Lymph Node Dissection (ALND)

The axillary lymph nodes run from the breast tissue into the armpit. This area under the arm is called the axilla.

Anywhere from 10 to 40 lymph nodes are removed and examined during an axillary lymph node dissection. These nodes are typically removed during your lumpectomy or mastectomy.

Lymph Node Status and Breast Cancer Treatment

The biopsy results, which is called a pathology report, will show how many lymph nodes were removed and how many were “involved” (tested positive for cancer). This is referred to as lymph node status.

Breast cancer that has not spread to nearby lymph nodes, is referred to as node-negative status. If the report indicates that cancer is present in the lymph nodes, this is referred to as node-positive status. Positive results also mean that the cancer may have already or could possibly spread to other organs, such as the bones, liver, lungs, and brain. In order to determine that, further tests would be necessary.

How much cancer is in each node will also show on the results of the report. Cancer cells can range from small in size and few in number to large in size and many in number. This information may be reported as: 

• Microscopic (or minimal), meaning only a few cancer cells are in the node and that a microscope is needed to find them.
• Gross (also called significant or macroscopic), meaning there is a lot of cancer in the node and that it can be seen or felt without the use of a microscope.
• Extracapsular extension, meaning the cancer has spread (metastasized) outside the wall of the node.

Breast cancer treatment decisions and prognosis (outlook) can be affected by the lymph node status. If there is cancer found in the lymph nodes, chemotherapy might be required in addition to surgery. This is because chemotherapy can attack cancer cells throughout the lymph system. Patients who have negative results often have a greater chance of a full and long-lasting recovery than patients who have positive results. This is why doing self-exams and getting your regular mammograms can be helpful in finding breast cancer early. The earlier it is found, the less chance there is of it spreading to the lymph nodes.