During surgery for invasive breast cancer (and sometimes for ductal carcinoma in situ (DCIS)), one or more lymph nodes in the underarm area (axillary lymph nodes) are removed to check for cancer cells.
The surgeon will likely make a separate incision (cut) in the underarm area (below where your underarm hair grows) to remove these nodes.
The figure below shows the location of the axillary nodes.
If breast cancer spreads, the axillary nodes are the first place it’s likely to go.
The presence or absence of cancer in these nodes is an important factor affecting cancer stage and prognosis.
To see if cancer has spread to the axillary lymph nodes, most people have a procedure called sentinel node biopsy.
Before or during this procedure, a radioactive substance (called a tracer) and/or a blue dye is injected into the breast.
The first lymph node(s) to absorb the tracer or dye is called the sentinel node(s). This is also the first lymph node(s) where breast cancer is likely to spread.
The surgeon locates the sentinel node(s) by looking for the lymph node that has absorbed the tracer (using a special device called a gamma probe) or the dye (which turns the lymph node(s) blue).
The radioactive tracer or blue dye usually identifies 1-5 nodes as the sentinel nodes. The surgeon removes the sentinel node(s) and sends them to a pathologist.
When the surgeon removes sentinel nodes, it doesn’t mean there’s cancer in the nodes. It just means a pathologist needs to check the nodes for cancer.
Lymph node-negative. No cancer is found in the sentinel nodes. It’s unlikely other lymph nodes have cancer.
Surgery to remove more lymph nodes will not be needed.
Lymph node-positive. Cancer is found in the sentinel nodes.
More lymph nodes may be removed with a procedure called axillary dissection. The goals of axillary dissection are to check how many lymph nodes have cancer and to reduce the chances of cancer returning in the lymph nodes.
Some women with 1-2 positive sentinel nodes who have a lumpectomy and will have whole breast radiation therapy may not need axillary dissection . (Whole breast radiation therapy treats part of the underarm area as well as the breast.)
Most people with 1 or more positive sentinel nodes who have a mastectomy will need an axillary dissection.
If you have a positive sentinel lymph node, talk with your health care team about whether you need an axillary dissection.
The most common technique to assess pathologic lymph node status is H&E staining.
In the past, some centers used immunohistochemistry (IHC) to look for cancer in the sentinel lymph node(s) that was too small to see with a microscope.
However, studies have shown the small deposits of tumor cells identified by IHC are not useful in prognosis [18-19]. So, many centers no longer use IHC to test sentinel lymph nodes .
Axillary dissection removes more lymph nodes than a sentinel node biopsy does. Because it disrupts more of the normal tissue in the underarm area, axillary dissection is more likely to affect arm function and cause lymphedema.
For this reason, sentinel node biopsy is the preferred first step to check the axillary lymph nodes.
In some cases, an axillary dissection instead of a sentinel node biopsy is advised.
This usually occurs when:
Learn more about axillary lymph nodes.
Axillary Lymph Nodes