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Sentinel lymph node biopsy

How to prepare for a sentinel lymph node biopsy, what happens and what happens after.

What a lymph node is

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 this test

The most common place that melanoma skin cancer spreads to is the nearby lymph nodes. Your specialist might offer you a sentinel lymph node biopsy, if your melanoma is deeper than 1mm (stage 1B to 2C). This is a test to find the first lymph node or nodes that a melanoma may spread to, and then check for cancer cells.

You have a sentinel lymph node biopsy (SLNB) at the same time as your operation to remove tissue around the melanoma (wide local excision).

Before your sentinel lymph node biopsy

The day before or morning of your wide local excision, you have a scan to show where the sentinel nodes are. You have the scan in the nuclear medicine department of the hospital.

You lie down on the treatment couch. You have small injections of a slightly radioactive liquid into the area where your melanoma was.

About 15 minutes later, you have a scan. This picks up the radioactive liquid and traces it as it moves through the lymphatic vessels and into the lymph nodes. The first nodes that the tracer drains into are the sentinel nodes. The radiographer marks where these nodes are on your skin.

The scan takes about 90 minutes or more, depending on where the melanoma is and where the sentinel nodes are.

What happens

You have the sentinel lymph node biopsy under general anaesthetic. While you are asleep, the surgeon injects a blue dye into the area around the site of the melanoma. The dye will gradually drain into the sentinel nodes.

Your surgeon uses a handheld scanner to pick up the radioactivity in the sentinel lymph nodes. They make a cut into your skin over the area. They can see the blue dye, which also helps them identify the sentinel nodes. They remove these nodes and send them to the laboratory to see if they contain cancer cells.

The surgeon then continues with the operation to remove more tissue around the site of the melanoma (wide local excision).

They stitch the wounds closed and cover with a small dressing. They may leave a thin tube where they took out the lymph nodes. This is to drain fluid that may collect there.

The blue dye will make your urine look blue or green for the next couple of days. This is harmless.

After your sentinel lymph node biopsy

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

As you have had 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 remove it the next day unless it is still draining a lot of fluid. Once they have taken this out, they will check your wounds and then you can go home.

About a week later, you have an appointment at the clinic or your GP surgery to have your stitches taken out, if needed.

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 contact details for a specialist cancer nurse. You can get in touch with them for information and support if you need to. It may help to talk to a close friend or relative about how you feel.

You can also call the Cancer Research UK nurses on freephone 0808 800 4040. The lines are open from 9am to 5pm, Monday to Friday.

What happens next

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

A positive result is if there are cancer cells in the sentinel nodes. This means the cancer has started to spread. Your doctor may offer you surgery to remove all the lymph nodes in the area. You’ll also have scans to see if the cancer has spread anywhere else.

Possible risks of a sentinel lymph node biopsy

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. Your doctors will make sure the benefits of having this test outweigh these possible risks.

You may have pain around the site of the sentinel lymph nodes. This might last up to 2 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 need antibiotics.

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 nurse may need to drain it with a needle and syringe.

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 or nurse can drain the swelling.

Some people may develop scar tissue in their arm or leg, depending 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.

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

If your surgeon removes sentinel nodes from under your armpit, you may develop swelling in your hand or arm. If they take 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.

Advantages and disadvantages of sentinel lymph node biopsy

Sentinel lymph node biopsy for melanoma is a relatively new test and is still unclear how useful it is. The National Institute for Health and Care Excellence (NICE) has produced guidelines about the diagnosis and treatment of melanoma. They list some advantages and disadvantages of this test. You can talk to your doctor about sentinel node biopsy. They can help you decide whether or not to have this test.


  • It can help doctors find out whether melanoma has spread to nearby lymph nodes, so they can remove them.
  • It is better than an ultrasound scan at finding very small cancers.
  • Doctors 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 operation.
  • The operation has possible risks, such as infection or collection of fluid under the wound.

The Option Grid website provides information to help people make decisions about their treatment.  

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