The Who, What, Where, When and Sometimes, Why.

Assessing Lymph Nodes

If breast cancer spreads, the axillary lymph nodes (lymph nodes in the underarm area) are the first place it’s likely to go. The presence or absence of cancer in these nodes affects breast cancer stage and the chances for survival.

During surgery for invasive breast cancer, and sometimes for ductal carcinoma in situ (DCIS), one or more axillary lymph nodes are removed. A pathologist checks whether or not these nodes contain cancer cells.

The surgeon will likely make a separate incision (cut) in the underarm area (below where your underarm hair grows) to remove the axillary lymph nodes.

The following is a 3D interactive model showing the parts of the breast, including the location of the axillary lymph nodes where breast cancer can spread.

Sentinel lymph node biopsy

To check if cancer has spread to the axillary lymph nodes, most people have a procedure called sentinel lymph node biopsy during breast surgery.

Before or during this procedure, a radioactive substance called a tracer and/or a blue dye is injected into the breast.

The first axillary lymph nodes to absorb the tracer or dye are called the sentinel lymph nodes. These are also the first lymph nodes where breast cancer is likely to spread.

The surgeon locates the sentinel lymph nodes by looking for the lymph nodes that have absorbed the tracer (using a special device called a gamma probe) or the dye (which turns the lymph nodes blue).

The radioactive tracer or blue dye usually identifies 1-5 nodes as the sentinel lymph nodes. The surgeon removes the sentinel lymph nodes and sends them to a pathologist.

If the surgeon removes sentinel lymph nodes, it doesn’t mean there’s cancer in the nodes. It just means a pathologist needs to check the nodes for cancer.

Findings from a sentinel lymph node biopsy

Lymph node status shows whether or not breast cancer has spread to the axillary lymph nodes.

  • Lymph node-negative means none of the sentinel lymph nodes contain cancer. So, it’s unlikely other lymph nodes have cancer. Surgery to remove more lymph nodes won’t be needed.
  • Lymph node-positive means at least one sentinel lymph node contains cancer. More lymph nodes may be removed with a procedure called axillary lymph node dissection. The goals of axillary lymph node dissection are to check how many lymph nodes have cancer and to reduce the chances of cancer returning in the lymph nodes.

When is axillary lymph node dissection needed?

Some women with 1-2 positive sentinel lymph nodes who have a lumpectomy and will have whole breast radiation therapy may not need axillary lymph node dissection [109]. (Whole breast radiation therapy treats part of the underarm area as well as the breast.)

Most people with one or more positive sentinel lymph nodes who have a mastectomy will need an axillary lymph node dissection or radiation therapy to the axillary lymph nodes [109].

If you have a positive sentinel lymph node, talk with your health care team about whether you need an axillary lymph node dissection.

Pathology techniques

The most common way to assess pathologic lymph node status is a lab test called H&E staining.

In the past, a lab test called immunohistochemistry (IHC) was sometimes used to assess lymph node status. However, studies showed the small deposits of tumor cells identified by IHC were not useful in prognosis [15-16]. IHC is only recommended for assessing lymph node status when the results of H&E staining are uncertain and sometimes, after neoadjuvant therapy [109].

Axillary lymph node dissection, sentinel lymph node biopsy and risk of lymphedema

Axillary lymph node dissection removes more axillary lymph nodes than a sentinel lymph node biopsy does. Because it disrupts more of the normal tissue in the underarm area, axillary lymph node dissection is more likely to affect arm function and cause lymphedema.  

For this reason, sentinel lymph node biopsy is the preferred first step to check the axillary lymph nodes.

Who cannot have a sentinel lymph node biopsy?

In some cases, a sentinel lymph node biopsy is not advised, and an axillary lymph node dissection is done instead.  

This most often occurs when:

  • A person can’t have a sentinel lymph node biopsy (for example, an axillary lymph node dissection has been done in the past).
  • The sentinel lymph node(s) can’t be found.
  • The axillary lymph nodes are already known to contain cancer (for example, before surgery, a health care provider felt suspicious lymph nodes and a needle biopsy showed they contained cancer).

Learn more about axillary lymph nodes

Learn about lymph node status and breast cancer stage.

Updated 04/07/24