What To Expect During a Sentinel Node Biopsy

sentinel lymph node illustration
Illustration @ A. D. A. M.

If you will be having surgery for breast cancer, your surgeon may recommend that you have a sentinel node biopsy at the same time. This procedure is done in order to determine whether your cancer may have spread beyond your breast into your lymph nodes. Since treatment recommendations differ with regard to whether your lymph nodes are negative or positive for metastases (spread) this is an important test. What can you expect during your sentinel node biopsy and what do the results mean? Let's take a step by step look at this test.

An Important Diagnostic Test

A sentinel node biopsy is a surgical diagnostic procedure done to remove a small sample of lymph nodes so they can be tested for breast cancer cells (metastases). The sentinel nodes are the first lymph nodes a breast cancer would be expected to spread to, and are examined to see if your cancer has spread beyond your original tumor.

If no other surgery is being done at the same time, this is an outpatient procedure and is important in staging of your breast cancer. If you are having a lumpectomy or mastectomy, a sentinel node biopsy may be done along with that procedure. Accurate staging, in turn, will help you and your doctor choose the best treatment options or your breast cancer.

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Steps Involved

There are several steps involved in order to determine which lymph nodes are your sentinel nodes, mark these in some way, and then test these nodes. The entire procedure takes up to several hours from the time you arrive to the time you have your results. Here are the steps you can expect.

Getting Started With Medical Imaging

Before your procedure, your surgeon will need to know the location of both your tumor and the sentinel lymph nodes. A combination of imaging techniques will be used to find and mark these locations before surgery.

Finding the Tumor

You will go to the Nuclear Medicine Department of the hospital or clinic where your sentinel node biopsy will be done. As you would for a mammogram or breast ultrasound, you will undress from the waist up, and put on a hospital gown. Next, you will lie down on an exam table. A radiology technician will use an ultrasound machine to find your tumor. The tumor site will be marked on your skin, so your surgeon can easily find it.

Anesthesia and Injection of the Dye and Tracer

A radiologist or nuclear medicine specialist will numb the area over your breast tumor. This may be done with a topical lidocaine patch (since this is a very tender area) followed by injection of lidocaine in your breast. When you are sufficiently numb, she will inject a weak radioactive dye (technetium-labeled sulfur colloid) and a blue dye (isosulfan blue) into the tumor site. The injection takes longer than a flu shot generally does and you may need several injections. In other words, you may wish to seriously ask for the numbing medication even if you think it will be very tolerable.

Lymph Node Mapping

Once injected, the dyes need some time to travel from your tumor site to your lymph nodes. Once in the tumor site, the dyes must be picked up by the small lymphatic channels that travel to the lymph nodes. You will spend some time in a nearby waiting room, so bring along some reading material or music. When the dyes have reached their destination, you are asked to return to the Nuclear Medicine Department and lie down on the exam table again. Imaging studies (lymphoscintigraphy) will be done to show which clump of lymph nodes is receiving the dyes, and that indicates where your sentinel lymph node will be found. The technician will mark this location on your skin, so your surgeon will know where to start looking.

Removing the Sentinel Lymph Node

You will be brought into the operating room, where your surgeon will be ready to begin after you are given a general anesthetic. The surgeon will use a hand-held probe to find the lymph nodes that contain the most radioactive dye. In that location, your surgeon will make a small curved incision, and look for the lymph nodes that have been stained with blue dye. Only one to three nodes will be removed unless many more are stained. These nodes are sent to the pathology department, where they are examined for metastasis and micrometastasis. Your incision will be closed and dressed, and you will be taken to Recovery.

Testing in Pathology

Once in the pathology lab, your nodes will be tested for cancer. Sometimes your surgeon will order a frozen section test for the nodes, in order to get results right then. If your nodes do contain cancer cells, you may have a full lymph node dissection immediately, to find the full extent of lymph node involvement. If a frozen section is not ordered, and your nodes contain cancer, a full lymph node dissection may be done later.

Recovering From Your Sentinel Node Biopsy

If blue dyes were used to find your sentinel lymph node, expect to see blue dye in your urine for about 24 hours. Sometimes there will be some bruising and blue dye on the skin around the incision. You will have a dressing and sutures to keep dry and may need pain medications until healing begins. Use your surgery-side arm gently (no lifting!) for at least a week after the procedure. The stains from the blue dye will diminish and your bruises will heal; the incision itself will fade to a fine line over time.

Getting Your Biopsy Results

Your surgeon or oncologist will call you about results of the biopsy as soon as the pathologist has completed her analysis. The report will include information on how many, if any, lymph nodes contain cancer cells. Ask for a copy of your pathology report and keep it with your health records. If a node contains cancer, it is diagnosed as positive, and if no cancer is found in a node, it is diagnosed as negative. A diagnosis of positive lymph nodes means that your cancer has spread (metastasized) beyond the original tumor. These results will affect the staging and treatment needed to treat your breast cancer.

When we talk about metastases to lymph nodes this does not mean a person has metastatic cancer. In fact, early-stage breast cancers such as stage 1A can have micrometastases to lymph nodes. The spread of breast cancer to lymph nodes does not mean that you have metastatic breast cancer, but only that your tumor has shown an "intent" to spread beyond the breast and lymph nodes.

Risks and Side Effects

Most of the side effects of a sentinel node biopsy are relatively minor. It can be uncomfortable when the dye or tracer is injected. The procedure can also add up to several hours to the already full day of your breast cancer surgery.

Possible risks of the procedure include lymphedema and the risk of false negative. These are discussed further here.


A common result of a full lymph node dissection is a condition called lymphedema. Because lymph nodes in your armpit area are missing, the lymph fluid that is usually processed there can build up and cause swelling. If this persists or increases, it can become painful. However, if you require only a sentinel node biopsy, you will still have enough nodes to handle the lymph fluid that travels through your armpit region, so the rate of lymphedema in that case, is only about five percent. In fact, much of the reason behind doing sentinel node biopsies instead of full lymph node dissections is to avoid lymphedema if possible.

False Negatives

Lymph nodes can vary in size, some small as a pinhead, others larger than a bean. Your surgeon will be hunting through skin and fat, looking for blue-dyed nodes, and must use some skill and judgment. It's possible that the sentinel node will test negative (clear of cancer), but cancer may be in some other lymph nodes. This is called a false negative. To protect you from false results, your surgical and pathology teams will follow strict guidelines, and if the results are in any doubt, more nodes will be removed and tested, to make sure of accurate results.

Bottom Line

Having a sentinel node biopsy requires several steps and you may wonder why all of the effort is needed. Choosing the best treatments for breast cancer requires accurate staging, and to accurately stage a breast cancer requires knowing whether any cancer has spread to the lymph nodes. In addition, determining if any lymph node involvement has micrometastases or macrometastases as well. The day of your biopsy may seem long, but the results will be significant in the days and months to come.

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