Sentinel lymph node biopsy for melanoma skin cancer

Sentinel lymph nodes are the first lymph node or nodes that a cancer may spread to. A sentinel lymph node biopsy is a test to find these lymph nodes. Your doctor then checks to see they have cancer cells in them. 

If your doctor thinks you need a sentinel lymph node biopsy, you have it at the same time as an operation to remove the skin and tissue around where the melanoma was. This operation is called a wide local excision.

What is a lymph node?

A lymph node is part of the lymphatic system. This is a network of thin tubes (vessels) and nodes that carry a clear fluid called lymph around the body. This is an important part of the immune system. It plays a role in fighting infection and destroying old or abnormal cells.

The nodes are bean shaped structures that filter the lymph fluid and trap bacteria and viruses, and cancer cells.

Diagram showing a lymph node

Why you might have a sentinel lymph node biopsy

The most common place that melanoma skin cancer spreads to is the nearby lymph nodes. You might have a sentinel lymph node biopsy if your doctor wants to check whether your nearby lymph nodes contain cancer cells.

Not everyone with melanoma skin cancer needs a sentinel lymph node biopsy - it depends on the size of the melanoma when you were diagnosed.

But your doctor might offer you one if the melanoma is:

  • between 0.8mm and 1mm thick and you have at least one other risk factor
  • less than 1mm thick and they think you would benefit from a biopsy
  • more than 1mm thick (stage 1B to 2C)

The other risk factors are:

  • broken skin on the melanoma (ulcer)
  • cancer cells in the lymph vessels or blood vessels of the melanoma
  • if the cancer cells are dividing quickly

Advantages and disadvantages of having a sentinel lymph node biopsy

Your doctor may offer you a sentinel lymph node biopsy if you have an early stage melanoma skin cancer. You can talk to your doctor about it. They can help you decide whether or not to have this test.


  • It can help your doctor find out if the melanoma has spread to nearby lymph nodes, so they can offer you treatment for this.

  • It's better than an ultrasound scan at finding very small cancers.

  • Your doctor can use the results to give you more information about what might happen to you in the future.

  • You may be able to take part in clinical trials looking at new treatments (you may not be able to take part in these trials if you haven't had a sentinel lymph node biopsy).


  • It isn't a cure for your melanoma, and there is no good evidence that people who have a sentinel lymph node biopsy live longer than those who don't have it.

  • The results don't always predict what might happen to you in the future.

  • You need to have a general anaesthetic to have the biopsy.

  • The biopsy has possible risks, such as infection or collection of fluid under the wound.

Before your sentinel lymph node biopsy

You normally have a sentinel lymph node biopsy at the same time as the wide local excision operation. You have it under a general anaesthetic, which means you will be asleep. You usually have an appointment at the pre assessment clinic beforehand.

You also have a special scan called a lymphoscintigram before you have a sentinel lymph node biopsy.

Pre assessment clinic

Your pre assessment appointment prepares you for your operation. This usually happens in the 2 weeks before your surgery.

At your appointment the pre assessment team may:

  • ask you questions about your health and any medicines you are taking
  • tell you when to stop eating and drinking before your operation
  • tell you if you need to stop taking any medicines before the operation
  • check your weight, blood pressure, pulse and temperature
  • ask what help and support you have at home

The pre assessment team will tell you how to prepare for your operation. What you need to do depends on what operation you are having.

They may also give you a leaflet about breathing and leg exercises to do after your operation. This is to help prevent chest infections and blood clots.

It helps to write down any questions you have and take them with you. The more you know about what is going to happen, the less frightening it will seem. You can ask more questions when you go into hospital so don’t worry if you forget to ask some.

Having a lymphoscintigram

A lymphoscintigram is a scan that shows where your sentinel lymph nodes are. It doesn't show if there is cancer in them. It helps your doctor find the sentinel lymph nodes during your biopsy.  

You have a lymphoscintigram in the nuclear medicine department of the hospital. You normally have it either:

  • on the day before your biopsy and operation
  • the morning of your biopsy and operation

When you go for the scan, you lie down on the treatment couch. Your doctor injects a small amount of radioactive liquid (tracer) into the area where the melanoma was. The tracer moves through the lymphatic vessels and into the lymph nodes.  

After you've had the tracer you have the scan. You have to have to keep very still while you go through the scanner. Let your radiographer know beforehand if you think this will be a problem for you. Tell them if you start to feel closed in or claustrophobic. They can help to reassure you.

The scan shows the first nodes that the tracer drains into. These are the sentinel lymph nodes. The radiographer marks where these nodes are on your skin. They may mark more than one place.

You usually go back to the ward after the scan until it's time for your biopsy and operation.

What happens during your sentinel lymph node biopsy

Your ward nurses will prepare you for the biopsy and operation. They ask you to wear a hospital gown and normally some socks. The socks help stop you getting a blood clot.

In the operating theatre your anaesthetist normally gives you a general anaesthetic. This makes you go to sleep.

Your doctor injects a blue dye into the area around where the melanoma was. The dye gradually drains into the sentinel nodes. This helps your doctor find them. They also use a handheld scanner. This picks up the radioactivity from the tracer that was injected during the lymphoscintigram.

Once they have found the sentinel lymph nodes they make a cut over them and take them out. They may leave a thin tube (drain) in the area afterwards. This is to drain any fluid that may collect there.

The lymph nodes are sent to the laboratory to see if they contain cancer cells.

At the end of the biopsy, your doctor stitches the wound closed and covers it with a small dressing. The stitches may need removing, or they may dissolve on their own. Your doctor or nurse will tell you which type of stitches they are.

Your doctor will do your wide local excision operation.

After your sentinel lymph node biopsy

You can usually go home later the same day if you don't have a drain. But it  also depends on the type of operation you had for the wide local excision. 

After a general anaesthetic, you will need someone to take you home and stay with you for 24 hours after the operation.

If you have a drain, your nurse will normally take it out the next day unless it is still draining a lot of fluid. Once it's out, they will check your wounds and you can go home.

The blue dye will make your skin look discoloured, especially around the area where they removed the sentinel lymph node. This will gradually fade. Your urine may also look blue or green for the next couple of days. This is harmless.

About a week later, you have an appointment at the hospital or your GP surgery. This is to have your stitches taken out if they need removing.

Possible risks of a sentinel lymph node biopsy

As with any medical procedure there are possible side effects or complications. Your doctor makes sure the benefit of the treatment outweighs these risks.

Everyone is different and side effects can vary from person to person. You may not have all the effects mentioned. Side effects and complications can include:

Allergic reaction

There is a small risk of having an allergic reaction to the blue dye. This can cause a rash, shortness of breath, redness or swelling of the face, and dizziness. Some allergic reactions can be life-threatening.

Tell your nurse or doctor straight away if you notice any of these symptoms while you are in the hospital or call 999 (emergency services) if you are at home.


You may have pain where you had the biopsy. This might last a few weeks. Taking mild painkillers can help. You might also feel stiff or tight around the area. It usually gets better over 6 weeks.


Contact your GP or the hospital if you have a high temperature or feel unwell. Or if your wound looks red, swollen or is leaking fluid (discharge). You might have an infection and need antibiotics.

Fluid collection (seroma)

Fluid collecting near the wound can cause swelling and pain. It also increases the risk of infection. The fluid normally goes away on its own within a few weeks. Your doctor may need to drain it with a needle and syringe.

Blood collecting near the wound (haematoma)

Occasionally blood collects in the tissues around the wound. This can cause pain and swelling, and the area may feel hard.

It normally goes away on its own, but can take a few months. If necessary, your doctor can drain the swelling.

Scar tissue in the arm or leg (cording)

Some people develop scar tissue in their arm or leg after the sentinel lymph node biopsy. But this depends on where the lymph nodes were taken from. It can cause tightness and feel uncomfortable. 

It is usually temporary and will settle over the first few months.

Swelling (lymphoedema)

There is a small risk of developing lymphoedema. This is caused by lymph fluid that can’t drain away.

If your doctor removes sentinel lymph nodes from your armpit, you may develop swelling in your hand or arm. If they take sentinel lymph nodes from your groin, you may develop swelling in your leg.

This is usually temporary, but in a small number of people it can be permanent.

Tell your doctor or nurse as soon as possible if you get swelling, pain or tenderness in your arm, hand or leg.

A sentinel lymph node biopsy is normally a safe procedure but your nurse will tell you who to contact if you have any problems afterwards.

Getting your results

It takes 1 or 2 weeks to get the results. Your doctor will usually discuss them with you at your next clinic appointment.

Waiting for test results can be worrying. You might have the contact details for your  specialist cancer nurse (CNS). You can get in touch with them for information and support if you need to. Or it may help to talk to a close friend or relative about how you feel.

For support and information, you can also call the Cancer Research UK information nurses. They can give advice about who can help you and what kind of support is available. Freephone: 0808 800 4040 - Monday to Friday, 9am to 5pm

What happens next?

A negative result means there are no cancer cells in the sentinel lymph nodes. This means that the melanoma is unlikely to have spread to the other lymph nodes. So you won’t usually need any further tests or treatment.

A positive result means there are cancer cells in the sentinel lymph nodes. This means the cancer has started to spread. Your doctor will talk to you about further treatment. You’ll also have scans to see where the cancer has started to spread to.

  • Melanoma: assessment and management
    National Institute for Health and Care Excellence (NICE), 2015 (updated 2022)

  • The Royal Marsden Manual of Clinical and Cancer Nursing Procedures (10th edition, online)
    S Lister, J Hofland and H Grafton 
    Wiley Blackwell, 2020

  • SIGN 146: Cutaneous melanoma - A national clinical guideline
    Health Improvement Scotland, 2017 (updated 2023)

  • Complications of sentinel lymph node biopsy for melanoma - A systemic review of the literature
    JA Moody and others
    European Journal of Surgical Oncology, 2016. Volume 43, Issue 2, Page 270-277

  • Sentinel Node Biopsy Guideline
    Melanoma Focus
    Accessed March 2024

  • The information on this page is based on literature searches and specialist checking. We used many references and there are too many to list here. Please contact with details of the particular issue you are interested in if you need additional references for this information.

Last reviewed: 
02 Apr 2024
Next review due: 
02 Apr 2027

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