Sentinel Lymph Node Biopsy

Introduction

If you have been diagnosed with breast cancer, melanoma, or certain other cancers, one of the first questions your treatment team needs to answer is whether the cancer has spread beyond where it started. The lymphatic system — a network of vessels and small glands called lymph nodes that carry fluid through the body — is one of the main paths cancer cells use to travel. Knowing whether any lymph nodes contain cancer helps your team decide what treatment you need next.

For many years, surgeons removed large numbers of lymph nodes simply to check them. This worked, but it often left patients with long-term swelling and arm or leg problems. Sentinel lymph node biopsy was developed to give the same staging information with far less surgery. Instead of removing many nodes, the surgeon identifies the one or two nodes that the tumour drains into first — the “sentinel” nodes — and removes only those for testing.

This guide explains what sentinel lymph node biopsy involves, who it is offered to, how it is performed, what recovery looks like, what the results mean, and the risks to be aware of. It is written for patients who already have a cancer diagnosis and are planning the next step in their care.

What Is Sentinel Lymph Node Biopsy?

Sentinel lymph node biopsy, often shortened to SLNB, is a surgical procedure used to find out whether cancer has spread from a primary tumour into nearby lymph nodes. It is a key part of cancer staging — the process doctors use to describe how far a cancer has progressed.

The idea behind the procedure is straightforward. Lymph fluid from any part of the body drains in a predictable pattern. The first lymph node (or small group of nodes) that drains fluid from a tumour is called the sentinel node. If cancer cells have begun to spread through the lymphatic system, they almost always reach this sentinel node before they reach any others. By finding and testing only this node, surgeons can get a very accurate picture of whether the cancer has spread — without disturbing the rest of the lymph nodes.

SLNB serves both diagnostic and treatment-planning purposes. The results tell your team:

• The stage of your cancer
• Whether further surgery to remove more lymph nodes is needed
• Whether additional treatment, such as chemotherapy, radiation, hormone therapy, or immunotherapy, would be helpful
• Your overall prognosis (the likely course of the disease)

SLNB has become a standard part of cancer care for several cancer types, and major guideline groups including the National Comprehensive Cancer Network (NCCN), the American Society of Clinical Oncology (ASCO), and the European Society for Medical Oncology (ESMO) recommend it as the preferred method of staging the lymph nodes in eligible patients.

Why Is Sentinel Lymph Node Biopsy Performed?

SLNB is performed to answer one main question: has the cancer reached the lymph nodes? The answer changes everything about the treatment plan that follows. It is most commonly used in the following cancers.

Breast cancer

SLNB is the standard staging procedure for the underarm (axillary) lymph nodes in patients with early-stage breast cancer when the nodes do not appear involved on examination or imaging. It is typically done at the same time as breast-conserving surgery (lumpectomy) or mastectomy. Major societies including ASCO and NCCN endorse SLNB over full axillary lymph node dissection in this setting because it gives accurate staging with far fewer side effects.

Melanoma

For melanoma of intermediate thickness, and in some cases thin melanomas with worrying features, SLNB helps determine whether the disease has spread regionally. The result influences decisions about further surgery, follow-up imaging, and systemic therapies such as immunotherapy. Current ASCO and Society of Surgical Oncology guidance describes SLNB as the standard staging approach for these patients.

Gynaecologic cancers

SLNB is increasingly used in selected cancers of the vulva, cervix, and uterine lining (endometrium) when the disease appears confined. It can replace the more extensive lymph node dissections that were previously routine and reduce the risk of leg swelling (lymphedema) afterwards.

Head and neck cancers

For early-stage oral cavity cancers and some other head and neck tumours, SLNB is used to assess the neck lymph nodes when they look normal on examination and imaging. It helps avoid larger neck dissections in patients whose nodes turn out to be clear.

Other cancers

SLNB is used less commonly in some skin cancers other than melanoma, certain penile cancers, and some thyroid and gastrointestinal cancers in research or specialised settings.

Who Is a Candidate?

Whether SLNB is suitable depends on your specific cancer, its stage, and the appearance of your lymph nodes on examination and scans. Your surgical oncologist will assess your individual situation. In general, SLNB is offered when:

• The primary cancer has been confirmed by biopsy
• The lymph nodes draining the area do not feel enlarged on examination
• Imaging (ultrasound, CT, MRI, PET, or mammography depending on the cancer) does not show clearly abnormal lymph nodes
• You are well enough to have a general or regional anaesthetic

SLNB is generally not the first choice in the following situations, although the decision is always individual:

• Lymph nodes have already been shown to contain cancer on biopsy or imaging — in which case a more complete lymph node removal or other treatment is usually planned
• The cancer is locally advanced with obvious spread
• Previous surgery or radiation in the area has changed how lymph fluid drains, making accurate mapping unreliable
• Known severe allergy to the dye or tracer used for mapping (alternatives may be considered)
• Pregnancy — specific protocols apply and the tracer choice may change

The final decision about whether SLNB is right for you, and when it should be done, is made by your surgical oncology team based on guideline recommendations and your circumstances.

Alternatives to Sentinel Lymph Node Biopsy

Several other approaches exist for assessing or treating lymph nodes in cancer. Whether any of them is more suitable than SLNB depends on the cancer type, stage, and findings on imaging.

Axillary lymph node dissection (ALND)

This is the more extensive operation in which most or all of the lymph nodes in the underarm are removed. It used to be the standard for breast cancer staging. It is still used when nodes are known to be involved with cancer in larger amounts, or in certain other situations. It carries a substantially higher risk of arm lymphedema, numbness, and shoulder stiffness compared with SLNB.

Regional lymph node dissection in other cancers

For melanoma, completion lymph node dissection (removing the rest of the nodes in the basin after a positive sentinel node) was once routine. Recent evidence has changed practice, and many patients with a positive sentinel node now have careful ultrasound monitoring instead of immediate further surgery. Your team will explain which approach current guidelines support for your situation.

Imaging-based assessment

Ultrasound, CT, MRI, and PET scans can identify abnormal lymph nodes, but they cannot reliably detect very small amounts of cancer inside a node that looks normal in size and shape. For this reason, imaging alone is not enough to stage the nodes in early cancers when they appear normal on scans.

Fine-needle aspiration or core biopsy of suspicious nodes

If a lymph node looks abnormal on imaging, a needle biopsy can be done first. A positive needle biopsy may make SLNB unnecessary because the question (has it spread?) is already answered, and a more definitive lymph node operation can be planned.

Observation without lymph node surgery

In some very early cancers, particularly certain low-risk breast cancers in older patients, omitting lymph node surgery altogether is sometimes considered after careful discussion. This is a specific scenario discussed within current guideline frameworks and is not a routine alternative.

Preparing for Sentinel Lymph Node Biopsy

Preparation for SLNB is similar to preparation for many other day-case surgeries. Your team will guide you through the steps. Common parts of preparation include:

Clinical assessment

• A physical examination focusing on the tumour and the draining lymph node area
• Review of your imaging (mammogram, ultrasound, MRI, CT, or PET as appropriate)
• Review of biopsy results confirming the cancer
• Blood tests
• An anaesthetic assessment to check that you are fit for the planned anaesthesia

Medication review

You will be asked about all medications you take, including over-the-counter drugs, herbal remedies, and supplements. Blood thinners, anti-inflammatory drugs, and some herbal products may need to be paused before surgery to reduce bleeding risk. Do not stop any prescribed medication without your doctor’s advice.

Fasting

If a general anaesthetic is planned, you will usually be asked not to eat for several hours before surgery. The exact instructions depend on the timing of your operation.

Allergy and consent discussion

Because dye or a radioactive tracer is used to find the sentinel node, your team will check for any known allergies. They will also walk you through what the procedure involves, what the results may show, the chance that further surgery or treatment will be needed, and the risks. This is the time to ask any remaining questions.

Tracer injection

In many centres, the radioactive tracer (a very small, safe dose) is injected hours before surgery, sometimes the day before. A scan called a lymphoscintigraphy may be done to map where the tracer travels. The blue dye, if used, is usually injected in the operating room just before the surgery starts.

What Happens During Sentinel Lymph Node Biopsy

SLNB is most often performed under general anaesthesia, although for some patients local or regional anaesthesia with sedation may be possible. It is typically a short operation, often lasting between 30 and 60 minutes when done on its own. When combined with breast surgery, melanoma wide excision, or other cancer surgery, the overall operating time is longer.

Step 1: Lymphatic mapping

To find the sentinel node, surgeons rely on tracers that travel through the lymphatic system in the same way cancer cells would. Two main tracers are used, sometimes together:

• A radioactive tracer (often technetium-99m). This is injected near the tumour. A handheld probe used during surgery picks up the radioactive signal where the tracer collects in the sentinel node.
• A blue dye. This is injected near the tumour shortly before or during surgery and visibly stains the sentinel node blue, so the surgeon can see it.

Some centres also use newer tracers such as indocyanine green (a fluorescent dye seen with a special camera) or magnetic tracers. Using two methods together (dual mapping) has been shown to improve the chance of finding the sentinel node accurately.

Step 2: Identifying and removing the sentinel node

The surgeon makes a small incision over the area where the tracer signal is strongest — usually in the armpit for breast cancer, near the original melanoma for skin cancers, or in the groin or neck for other cancers depending on drainage. Using the gamma probe and looking for the blue staining, the surgeon identifies the sentinel node or nodes and carefully removes them. In most cases, one to three nodes are removed.

Step 3: Sending nodes to the laboratory

The removed nodes are sent to a pathologist for examination. Depending on the cancer type and centre, this may be done in two ways:

• Intraoperative testing (frozen section or imprint cytology). The pathologist examines the nodes while you are still in surgery. If cancer is found, the surgeon may go on to remove more lymph nodes during the same operation. This approach is used in some centres for some cancers.
• Postoperative testing only. The nodes are processed over the next few days using more detailed techniques. Final results are available later, and any further surgery is planned at a separate appointment if needed. This is the more common approach in many centres because the detailed processing is more sensitive.

Closing the wound

The small incision is closed with stitches or surgical glue, and a dressing is applied. A small drain is occasionally placed, although usually not for SLNB alone.

Recovery and Healing

Recovery from SLNB alone is generally quick. When it is combined with a larger cancer operation, recovery follows the timeline of the larger operation.

The first day

Most patients go home the same day or after a short overnight stay, depending on the combined surgery and local practice. You may feel groggy from the anaesthetic for a few hours. The wound site is usually sore but manageable with simple pain relief.

If a blue dye was used, do not be alarmed if:

• Your urine looks blue or green for one to two days
• Your skin near the injection site has a bluish stain that fades over weeks to months
• The whites of your eyes briefly look slightly tinted

These are expected effects of the dye and not a cause for concern.

The first week

• Mild to moderate soreness around the incision
• Some bruising or swelling
• Restricted movement on the side of the surgery (for example, arm movement after axillary SLNB)
• Need for simple pain relief such as paracetamol or other medication prescribed by your team

Two to four weeks

• The wound usually heals well
• Most patients return to light daily activities and desk-based work
• Driving is usually possible once you can move comfortably and react safely
• Heavier lifting and strenuous exercise are typically avoided for several weeks, especially if a larger operation was done at the same time

Understanding the Results

SLNB results usually take a few days to a couple of weeks, depending on the laboratory’s processing schedule.

Negative sentinel node

If no cancer is found in the sentinel node, the result is called negative. This strongly suggests that the rest of the lymph nodes are also clear, because cancer would almost always have reached the sentinel node first. In most cases, no further lymph node surgery is needed. The result may also reduce the need for, or change the type of, further treatment such as radiation or systemic therapy.

Positive sentinel node

• Macrometastasis — a deposit larger than 2 mm
• Micrometastasis — a deposit larger than 0.2 mm but not more than 2 mm
• Isolated tumour cells — very small clusters of 0.2 mm or less

What happens after a positive result depends on the cancer type, the size of the deposit, the type of primary surgery performed, and current guidelines. Options may include further lymph node surgery, radiation to the lymph node area, chemotherapy, hormone therapy, targeted therapy, or immunotherapy. For example, in breast cancer with limited sentinel node involvement after lumpectomy, current guidelines have moved away from automatic full axillary dissection in many situations. In melanoma, careful ultrasound surveillance is now often used instead of immediate completion lymph node dissection. Your team will discuss the options that fit your situation.

Accuracy of the test

SLNB is highly accurate in experienced hands. Across published studies, surgeons successfully identify the sentinel node in more than 95 percent of cases when modern dual mapping is used. The false-negative rate — the chance of missing cancer that is actually present in the lymph nodes — is low but not zero, typically in the range of 5 to 10 percent depending on the cancer type and technique. Your team will explain what this means for your follow-up plan.

Risks and Complications

SLNB is considered a safe procedure with fewer complications than full lymph node dissection. However, like any surgery, it carries some risks. Knowing what to expect can help you spot problems early.

Common, usually minor

• Pain and bruising at the wound site
• Temporary swelling
• Numbness or altered sensation near the wound, which may be permanent in a small area
• Blue staining of the skin and urine from the dye, fading over weeks to months

Less common

• Wound infection — usually treated with antibiotics
• Seroma — a collection of fluid under the skin that sometimes needs draining
• Bleeding or haematoma (a collection of blood) at the wound
• Shoulder stiffness or reduced range of motion after axillary SLNB

Lymphedema

Lymphedema is long-term swelling caused by disruption of lymph drainage. After SLNB, the risk is much lower than after full lymph node dissection. Reported rates of lymphedema after SLNB are typically in the range of 5 to 8 percent, compared with 15 to 30 percent or more after full axillary dissection. Lymphedema risk rises further when SLNB or dissection is combined with radiation to the lymph node area. Early movement, physiotherapy, weight management, and prompt attention to any infection on the affected limb can help lower the risk.

Allergic reaction to the dye or tracer

Allergic reactions to the blue dye are uncommon but can range from mild skin reactions to, very rarely, severe allergic reactions. Reactions to the radioactive tracer are rare. Your team will check for known allergies before surgery and is prepared to treat any reaction.

Failure to identify the sentinel node

In a small number of cases, no sentinel node can be identified during surgery. When this happens, your surgeon may proceed with a different lymph node approach — for example, a limited axillary sampling — based on the situation and the discussion you had before surgery.

Anaesthetic risks

Any general anaesthetic carries small risks, which the anaesthetic team will discuss with you. These risks are generally low for fit patients undergoing short procedures.

Life After Sentinel Lymph Node Biopsy

SLNB is one step in your overall cancer care. What life looks like afterwards depends mostly on the cancer being treated and the results.

Further treatment

Based on the SLNB result and other features of your cancer, your team will plan further treatment. This may include:

• Additional surgery, either to remove more lymph nodes or to complete the primary cancer operation
• Radiation therapy
• Chemotherapy
• Hormone therapy (for hormone-sensitive cancers such as some breast cancers)
• Targeted therapy or immunotherapy, depending on the cancer type and molecular features

Caring for the affected limb

If your SLNB involved the underarm or groin, looking after the arm or leg on that side helps reduce lymphedema risk and other problems. General advice often includes:

• Keeping the skin clean and moisturised to avoid cracks and infection
• Treating cuts, burns, and insect bites promptly
• Avoiding very tight clothing or jewellery on the affected limb
• Maintaining a healthy weight and being physically active
• Reporting any new swelling, heaviness, or skin changes to your team early

Your team may refer you to a lymphedema therapist for assessment, prevention advice, or treatment.

Follow-up

You will be followed up by your cancer team according to your specific diagnosis. This usually includes regular clinical examinations, imaging, and other tests at intervals decided by guidelines and your individual risk. The sentinel node result helps shape this follow-up plan.

Emotional impact

Waiting for results, processing a positive node, or adjusting to ongoing treatment can be emotionally hard. Many cancer centres offer counselling, support groups, and other resources. Telling your team how you are coping is as important as describing physical symptoms.

Frequently Asked Questions

Is sentinel lymph node biopsy painful?

The procedure itself is done under anaesthesia, so you do not feel it. Afterwards, most patients describe a mild to moderate soreness at the wound that is well controlled with simple pain medicines. Pain usually settles within a few days.

How long does it take to get the results?

If the laboratory does intraoperative testing, an initial result may be available during surgery. Final, more detailed results usually take several days to about two weeks, depending on the laboratory and processing techniques.

Why does my urine look blue or green after surgery?

This is from the blue dye used to mark the sentinel node. It is harmless and clears within one to two days.

Will I definitely need more surgery if the sentinel node is positive?

Not always. The decision depends on the cancer type, how much cancer was found in the node, the type of primary surgery you had, and current guidelines. For some patients — for example, some women with breast cancer who have had a lumpectomy and will receive radiation, or many patients with melanoma and a positive sentinel node — further lymph node surgery may not be needed and close monitoring may be used instead. Your team will explain the options for your situation.

Can sentinel lymph node biopsy miss cancer?

SLNB is highly accurate but not perfect. In a small percentage of cases, cancer in the lymph nodes can be missed (a false-negative result). Your follow-up plan is designed to detect any signs of spread early.

How is sentinel lymph node biopsy different from full lymph node dissection?

SLNB removes only the first one or two nodes that drain the tumour, while full lymph node dissection removes most or all of the nodes in an area such as the underarm or groin. SLNB has a much lower risk of lymphedema, numbness, and shoulder or leg problems and is now the preferred staging method in eligible patients.

Is the radioactive tracer safe?

Yes. The dose used for mapping is very small and clears from the body quickly. Any radiation exposure is far lower than for many routine scans.

Can the procedure be done during pregnancy?

SLNB can be considered in pregnancy in specific situations, particularly for breast cancer. The tracer choice and timing are adjusted, and the decision is made in close consultation with obstetric and oncology teams.

Is sentinel lymph node biopsy performed in children?

SLNB is overwhelmingly an adult procedure. It is occasionally used in older children and adolescents with melanoma or certain rare tumours, in specialised paediatric oncology centres. The principles are similar to adult care, adjusted for the child’s size and the specific cancer.

How soon will I know my full treatment plan?

After the SLNB results and other staging information are available, your case is usually discussed in a multidisciplinary team meeting. Your team will then meet you to explain the full plan, often within a few weeks of surgery.

Conclusion

Sentinel lymph node biopsy has changed the way cancer is staged. By focusing on the one or two lymph nodes most likely to show early spread, the procedure gives doctors the information they need to plan treatment while sparing many patients the long-term side effects of removing large numbers of nodes. For people with breast cancer, melanoma, and several other cancers, it has become a standard, well-studied part of care, supported by major guideline groups.

The procedure is short, generally safe, and followed by a quick recovery in most cases. The results, whether negative or positive, are an important step in shaping the rest of your treatment journey. Knowing what to expect — from preparation and mapping, through the operation itself, to recovery and the meaning of the results — can help you take that step with greater confidence and clearer questions for your team.