What Is a Sentinel Node Biopsy?

What to expect when undergoing this test

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

Sentinel node biopsy is a surgical procedure doctors use to see whether cancer has spread beyond the tumor and into the lymphatic system. It's often performed alongside surgery for breast cancer but may also be done on its own.

To help the surgeon find your lymph nodes, they're "marked" using a blue dye that'll be injected into your system before the procedure.

Purpose of Test

Treatment recommendations for breast cancer depend on whether your lymph nodes are negative or positive for metastases (spreading cancer), so this is an important test.

During a sentinel node biopsy, the surgeon removes a small sample of lymph nodes and sends to a lab so they can be tested for breast cancer cells. The sentinel nodes are the first lymph nodes a breast cancer is expected to move into.

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

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Risks and Contraindications

Possible risks of this procedure include lymphedema and false negatives. Few contraindications exist.


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 is only about five percent. In fact, much of the reason behind doing sentinel node biopsies instead of full lymph node dissection is to avoid lymphedema if possible.

False Negatives

Lymph nodes can vary in size, with some as small as a pinhead and others larger than a bean. Your surgeon will be hunting through skin and fat, looking for blue-dyed nodes, and must rely on 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 the diagnosis is correct.


Some people with breast cancer are not considered candidates for this procedure. They include those with:

  • Inflammatory breast disease
  • Clinically positive axillary nodes
  • Metastases confirmed by fine-needle aspiration

Axillary lymph node dissection is believed to be a better test for these forms of the disease.

Before the Test

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.


The entire procedure takes several hours from the time you arrive until the time you leave with your results.


Sentinel node biopsy is performed in the nuclear medicine departments of hospitals and surgery centers.

What to Wear

You'll need to wear a hospital gown for the procedure.

For going home afterward, especially if you're having breast cancer surgery along with the biopsy, you'll want to have a soft but supportive bra, such as a sports bra, and a button-down shirt, since you'll need to avoid lifting your arms for a while.

Food and Drink

You'll need to fast for 8 to 12 hours before surgery. Ask ahead of time about any medications that you can and can't take the morning of surgery.

Cost and Health Insurance

Check well ahead of time on the cost of your procedures and how they'll be covered so you don't have any nasty surprises the day-of or after your surgery.

Check with your insurance company to see what charges you may face and when they'll be due. Make sure to ask whether your policy covers your surgeon, anesthesiologist, the facility, and the tests that will be run on your tumor after it's removed.

If you have a co-pay, expect to pay it before surgery unless the facility tells you otherwise.

What to Bring

When you arrive at the facility, make sure you have your:

  • Insurance card
  • Identification
  • A way to pay your co-pay, if necessary
  • Any papers your doctor may have given you
  • List of current medications
  • Medical history
  • List of allergies, including medication, latex, and adhesives

You may want to bring a book or electronic device to occupy your time before the procedure and while waiting for the dye to circulate. If you'll be staying overnight, you'll need things like a toothbrush, a change of clothes, and anything you want to make yourself more comfortable, such as a pillow or slippers.

During the Test

Be sure to arrive early enough before your procedure to get checked in and fill out any necessary paperwork.


After you're called back, you'll be instructed to 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 and the tumor site will be marked on your skin, so your surgeon can find it easily.

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. It can become rather uncomfortable or painful.

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.

While this is happening, you'll likely be in a nearby waiting room, so bring along some reading material or music.

When the dyes have reached their destination, you'll go back in and lie on the exam table again. Imaging studies (lymphoscintigraphy) will be done to show which clump of lymph nodes is receiving the dyes, and that points the way to your sentinel lymph node.

Throughout the Test

You'll be given a general anesthetic. Once you're asleep, 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.


Once you're awake and alert, you'll either be moved to a hospital room (if you're staying overnight) or given follow-up instructions and discharged so you can go home.

After the Test

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.

Managing 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.

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'll have a dressing and sutures to keep the incision dry and may need pain medications for a few days. 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.

Interpreting Results

Your surgeon or oncologist will call you about the results of the biopsy as soon as the pathologist has completed the analysis. The report will include information on how many, if any, lymph nodes contain cancer cells.

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 your staging and the treatment you need.

When we talk about metastases to lymph nodes this does not mean a person has metastatic cancer. In fact, even 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.

Ask for a copy of your pathology report and keep it with your health records.


After your results are in, it's time to talk about what follow-up treatments you may need. Typically, after surgery, treatment options include:

A Word From Verywell

Having a sentinel node biopsy requires several steps and you may wonder why all of the efforts are needed. Choosing the best treatments for breast cancer requires accurate staging, and accurate staging requires knowing whether any cancer has spread to the lymph nodes.

In addition, determining if any lymph node involvement has micrometastases or macrometastases is crucial for making your future treatment decisions. 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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