What Is a Sentinel Node Biopsy?

A sentinel node biopsy is a surgical procedure used to look at a sample of tissue (biopsy) from your lymph nodes to see if an early-stage breast cancer has spread beyond the initial tumor. "Sentinel" means to guard or stand watch, so sentinel lymph nodes are the first ones a cancer is expected to be found in if it has spread (metastasized). Checking these lymph nodes can help your healthcare team identify your breast cancer stage and prescribe a treatment plan.

Evidence of cancer in the sentinel nodes means the risk of cancer spreading to other body parts is higher because cancer cells can spread via lymphatic fluid (lymph). Sentinel node biopsy is mainly used for breast cancer and melanoma. Scientists are investigating to determine the usefulness of this test for other cancers. 

Often, lymph node biopsy is performed alongside mastectomy (breast removal) or other breast cancer surgery. The biopsy may also be done as a standalone procedure. 

This article will discuss sentinel node biopsy, including the purpose, risks, contraindications, what to expect during the test, and how to understand your results.

Purpose of Test

During a sentinel node biopsy, your surgeon removes a small sample of lymph nodes and sends them to a lab so they can be tested for breast cancer cells. 

In early-stage breast cancer, treatment recommendations depend on whether your lymph nodes are negative or positive for metastases (spreading cancer). Accurate staging will help you and your healthcare provider choose the best options for you.

An alternate means of checking for cancer in the lymph nodes is axillary lymph node dissection. During this procedure, most of the lymph nodes in your armpit are removed and examined. This procedure may provide more evidence of whether cancer has spread.

Because sentinel node biopsy is less invasive, it is considered the standard of care when you have:

• Early-stage breast cancer that can be surgically removed
  AND
• Axillary lymph nodes that are not enlarged

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Risks and Contraindications

Sentinel node biopsy poses a 5% chance of causing lymphedema. When the lymph nodes are removed or damaged, lymph fluid can build up and cause swelling. Lymphedema can also lead to decreased mobility and pain.  

Sentinel node biopsy removes fewer nodes than a full lymph node dissection. Healthcare providers aim to avoid lymphedema by leaving behind enough nodes to handle the lymph fluid that travels through your armpit region.

Contraindications

Some people with breast cancer are not considered candidates for this sentinel node biopsy. Your healthcare provider may recommend axillary lymph node dissection instead of sentinel node biopsy when:

• Your tumor is large or cancer has spread throughout your breast
• You have inflammatory breast cancer
• You are pregnant
• Your clinically positive axillary (armpit) nodes are already confirmed
• You have had metastases confirmed by fine-needle aspiration

Before the Test

Typically, you will receive preparation instructions from your surgeon or the facility prior to your procedure, but a brief overview is provided here.

Timing

The entire procedure takes several hours from the time you arrive until you leave. If you are also having breast cancer surgery the same day, you may need to stay overnight.

Location

Sentinel node biopsy is performed in the nuclear medicine departments of hospitals and surgery centers. If only the biopsy is being done, it generally will be an outpatient procedure.  If you are having a lumpectomy or mastectomy, a sentinel node biopsy may be done at the same time as your breast surgery.

What to Wear

You will need to wear a hospital gown for the procedure, so wear clothing that is comfortable and easy to remove.

Plan ahead for the trip home. You will likely be sore, especially if you are having breast cancer surgery along with the biopsy. You may also need to avoid lifting your arms for a while. Be sure to bring:

• A soft but supportive bra, such as a sports bra 
• A button-down or zip-up shirt (avoid anything you would need to pull overhead)

Food and Drink

You will need to fast for eight to 12 hours before surgery. Ask ahead of time about taking any medications the morning of surgery. Your surgical team should review your medication list and give you specific instructions.

Cost and Health Insurance

Contact your insurance company well ahead of time about the cost of your procedure(s) and how they will be covered. Check with your insurance company to see what charges you may face and when they will be due. 

Ask about any necessary prior authorizations. 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 is removed.

What to Bring

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

• Insurance card
• Identification
• A way to pay your copay, if necessary
• Any papers your healthcare provider may have given you
• Radiology images if available (prior mammograms, CT scans, MRI)
• 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 will be staying overnight, you will need things like a toothbrush and a change of clothes. You may also wish to bring 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. Throughout this appointment, you will interact with a variety of healthcare professionals, including a nurse, a radiologist, and your surgeon.

Pre-Test

After you are called back, you will be instructed to change into 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 or cream (since this is a very tender area) followed by an injection of lidocaine in your breast. 

When you are sufficiently numb, they will inject a weak radioactive dye (technetium-labeled sulfur colloid) and/or a blue dye (isosulfan blue) into the tumor site. The dye moves long the lymphatic system and stains the lymph nodes. This helps the surgeon identify your sentinel nodes.

Lymph Node Mapping

Once injected, the dyes need some time to travel from your tumor site to your lymph nodes. The dyes are picked up by the small lymphatic channels and slowly move to the lymph nodes. Some people require several scans or a repeat injection during this process.

While this is happening, you will likely sit in a nearby waiting room, where you can do something relaxing to pass the time. Expect to wait 30 minutes to two hours for the dye to get to the nodes. 

When the dyes have reached their destination, you will go back in and lie on the exam table again. Imaging studies (lymphoscintigraphy) will be done to show which lymph nodes are receiving the dyes. These will guide the surgeon to your sentinel lymph nodes.

Throughout the Test

Once the lymph nodes have been identified, you will be prepared for the surgical part of your biopsy. You will be brought into the operating room and given a general anesthetic. Once you are asleep, the surgeon will use a hand-held probe to find the lymph nodes that contain the most radioactive dye.

Your surgeon will make a small curved incision over the target lymph nodes. They will look for the lymph nodes that have been stained with blue dye. Lymph nodes can vary in size, with some as small as a pinhead and others larger than a bean. 

Your surgeon will rely on skill and judgment as they hunt through skin and fat looking for dyed nodes. Typically, sentinel node biopsy takes about 45 minutes to an hour. Sometimes it may take longer if you have many lymph nodes that appear dyed or if you have additional surgeries on the same day. Your team should help you anticipate the length of your procedure. 

Often only one to three nodes will be removed unless many more are stained. The removed lymph 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.

Post-Test

You will stay in recovery until you are awake and alert, usually under an hour. 

If you are staying overnight, you will be moved to a hospital room. This is most common with larger surgeries or if you need to have a drain placed in the surgical area.

If you are able to go home, you will be given follow-up instructions and discharged. After general anesthesia, you will need someone to drive you home.

After the Test

Your surgeon will label your lymph nodes and send them to the pathology lab where they will be tested for cancer. Typically biopsy results are available in a few days but may take up to a week. Your surgical team will tell you when to expect your results and how you will receive them.

Sometimes your surgeon will order a frozen section test for the nodes in order to get results during your biopsy procedure. 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 to remove the cancerous lymph nodes.

Managing Side Effects

Your surgeon will suture (stitch shut) the incision. There will be a dressing in place to keep the area clean and dry. You may need pain medications for a few days.  

Use the arm on the side of your surgery gently for at least a week after the procedure. Avoid lifting anything. The incision itself will fade to a fine line over time.

Most of the side effects of a sentinel node biopsy are relatively minor. Expect the blue dye used during the procedure to show up in your urine for about 24 hours. Sometimes there will be some bruising and blue dye on the skin around the incision as well, which will typically diminish over time.

Possible side effects of sentinel lymph node biopsy include: 

• Lymphedema (swelling)
• Seroma (fluid collection)
• Incision side effects (numbness, tingling, swelling, bruising, pain at the site)
• Infection 
• Decreased motion at the surgical site
• Reactions to the dye (allergy)

Most side effects will go away over time without needing intervention.

Lymphedema may require treatment to help drain the swelling. Incision site effects typically fade over time, but the numbness may not go away if a nerve was damaged. Infections are typically treated with antibiotics. Movement improves over time, but may occasionally require physical therapy. A dye reaction should be evaluated by your healthcare team to determine the best course of treatment.

Interpreting Results

Your surgeon or oncologist will contact you about the results of the biopsy as soon as the pathologist has completed the analysis (which may be before your discharge if you are staying at a hospital). The time for biopsy results depends on the institution but typically you will have results in a few days to a week.

Your pathology report will include information on how many, if any, lymph nodes contain cancer cells. If a node contains cancer, it is diagnosed as positive. Otherwise, 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.

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

False Negatives

It is possible that the sentinel node will test negative (clear of cancer), but cancer may be in some other lymph nodes that were not tested. This is called a false negative. To protect you from false results, your surgical and pathology teams will follow strict guidelines. If the results are in any doubt, more nodes will be removed and tested to make sure the diagnosis is correct.

False Positives

Although not very common, it is possible for cells to be placed into the lymph node sample during other procedures like fine-needle aspiration or core biopsy. This results in a false-positive result. The sample shows cancer cells but cancer has not spread to the lymph nodes.

If cancerous cells are found on biopsy, the pathologist will typically run additional tests to help determine if your cancer has truly spread or if it is likely contamination from a procedure. Extra lymph nodes may also be removed and tested to better determine if cancer has metastasized to confirm the diagnosis. 

Follow-Up

After your results are in, it is time to talk about what follow-up treatments you may need. Typically, after surgery, treatment options for those who test positive include:

• Chemotherapy
• Radiation
• Targeted therapy
• Hormonal therapy

Summary

A sentinel lymph node biopsy can be an effective way to determine if and how far an early-stage breast cancer has spread. Dye is injected near the tumor and the lymph drainage helps to trace the path to the lymph nodes so they can be removed and examined.

Fewer nodes are removed than with a full lymph node dissection, so this approach typically has fewer side effects. This is a surgical procedure, so expect to be at the facility for several hours and allow adequate time for recovery.

A Word From Verywell

Having a sentinel node biopsy is a long procedure with several steps. 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.