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Sentinel Lymph Node Biopsy for Melanoma

Patient information A-Z


This information sheet explains the reasons for offering additional surgery for your recently diagnosed melanoma. It also describes what the procedure involves. It should be used as a guide only, to help you remember the points discussed with you in clinic.

Why is the procedure offered?

Melanoma is a type of skin cancer which occasionally can spread locally in the skin, and to other body organs. For this reason, we remove additional skin around the original melanoma scar (a “wide local excision”) and may offer a sentinel node biopsy. After the surgery to do this, you will have regular clinical follow up and, where indicated, scans for 5 years after diagnosis.

Wide Local Excision (“WLE”)

Performing a wider excision of the melanoma is an essential part of your melanoma treatment. This is to reduce the risk of it coming back in that area. The amount of skin removed is dictated generally by the original thickness of the melanoma (Breslow thickness) from the first biopsy, and are usually between 1 to 2 cm around the scar.

Sentinel Lymph Node Biopsy (“SLNB”)

The lymphatic system forms part of the body’s natural defences against infection and cancers. It is made up of tiny lymphatic vessels within your skin which then travel to lymph nodes, which commonly found in the neck, armpits and groin. These vary in size from a pea to a small walnut, and are often referred to as ‘glands’. There are over 300 lymph nodes spread across the body which filter the lymphatic fluid that travels through them, removing dying cells and bacteria.

It is relatively uncommon for melanoma to spread into other parts of the body without passing through a lymph node. The lymph node connected to the area of skin which originally had the melanoma is referred to as the “sentinel” lymph node. Occasionally this can be more than one lymph node, and can be in different areas of your body. The purpose of the SLNB is to accurately identify the location of the lymph node, remove it entirely, and use specialised examination to find microscopic amounts of melanoma.

SLNB is not a treatment, but does provide information about how your melanoma might behave in the future. If microscopic melanoma is identified in the lymph node, additional treatments may be discussed if appropriate.

How is the procedure performed?

The SLNB procedure involves three steps:

  1. A lymphoscintigram (an injection and scan in the Nuclear Medicine department)
  2. Blue dye lymphatic mapping (an injection in the Operating theatre after general anaesthetic)
  3. Removal of sentinel lymph nodes identified by the scans and mapping.

The WLE around the original melanoma scar is done under the same general anaesthetic.

1. Lymphoscintigram

This is a specialised scan and is also referred to as a lymphatic drainage scan or a lymphatic mapping test. You will be awake for the scan and it can take two to three hours. This is arranged for the morning of your surgery.

How is it done?

The site of the melanoma is marked and anaesthetic cream applied to the area. A tiny dose of radioactive tracer is injected into the skin around the melanoma scar. This tracer moves through the skin’s lymphatic channels to the sentinel lymph nodes over several minutes. Scans are done to detect radioactivity in the sentinel lymph nodes. You may additionally have a CT scan to help identify the exact location of the lymph nodes in some areas.

Although the tracer is radioactive there is no significant health risks to you from its use. The dose used is very small and it loses radioactivity very quickly. Most tracer remains in the skin and sentinel lymph nodes, which are removed during the surgery. Any remaining tracer naturally decays within 1-2 days. The location of sentinel lymph nodes identified will be marked on the skin to aid the surgeon.

Are there any side effects?

The scan could cause slight pain at the injection site. You may also have some redness at the injection site for an hour or so afterwards.

2. Blue dye lymphatic mapping

This is performed in the operating theatre under a general anaesthetic. When you are anaesthetised (asleep), a blue dye is injected into the skin around the scar of the original melanoma. This dye rapidly moves through the lymphatic channels and accumulates in the sentinel lymph nodes. The blue colour assists the surgeon in finding the sentinel lymph nodes more easily.

Are there any side effects?

This procedure may leave blue discolouration of the skin. However, the stained skin is usually removed completely as part of the WLE. Any remaining dye is usually removed through your urine, causing occasional blue/green discolouration for up to 2 days after the surgery. Rarely, you may have an allergic reaction to the blue dye (less than 1 in 1000 patients) and will be treated immediately.

3. Removal of Sentinel lymph nodes

After the blue dye injection, the SLNB will be done. This consists of removing the sentinel lymph nodes for detailed microscopic examination in the pathology department. This is done at the same time as the WLE. A cut is made over the marked lymph node area(s) identified by the nuclear medicine scan. Rarely, the sentinel lymph node is not found on the scan or at surgery. If this happens, a WLE alone is done, and your surgeon will discuss this with you.

Are there any side effects?

The side effects after a SLNB may include pain or discomfort, loss of sensation in and around the site of surgery, small fluid collection (seroma), redness or infection at the surgical scars. Less common side effects could include swelling of the limb or area nearest the surgery which is transient in most cases, but rarely can be permanent (lymphoedema).

Wide local excision of the melanoma scar

This is undertaken under general anaesthetic at the same time as the SLNB. This involves removing further tissue from around the original area of melanoma, reducing the risk of melanoma returning at that site in the future. Once the area is removed, plastic surgery reconstruction may be required. Your surgeon will discuss this with you before the surgery.

When am I able to resume my usual activities?

Bathing / showering

You may have a shower a few days after surgery. Avoid having a bath until the wounds are fully healed and the stitches or staples are removed.

When washing, keep the dressing dry by washing around the dressings. If the dressing becomes wet, remove it completely, and clean the area with water. Dry it thoroughly with a clean towel or a hairdryer, before applying a clean dressing. Avoid extreme temperatures when bathing. Please do not use steam rooms or saunas.


You will be able to start work again once you feel up to it but if your job involves a lot of lifting or heavy work this will take longer. A medical certificate can be provided by the hospital whilst you are an inpatient. Once you are discharged, speak to your GP who will give you a medical certificate to cover until you are fit to go back to work.


You are unable to drive for 48 hours following a general anaesthetic due to insurance. You will be able to start driving once you feel up to it and you are able to perform an emergency stop comfortably. Do not drive if you are unwell and unable to take emergency action. It is advisable to check with your insurance company before you start driving again.


It can take between four to six weeks for the results to be available. We will phone you with the results, or arrange an outpatient appointment if you prefer. If microscopic melanoma is identified, your surgeon will discuss future management options with you. It may be advised that you continue under regular skin surveillance with additional CT scans or ultrasound scans. Alternatively, they may recommend you see an oncology consultant about having drug therapy. This is called adjuvant therapy, and reduces the risk of melanoma coming back.

If your results come back as negative (no evidence of melanoma) you will continue to have regular outpatient visits for skin and lymph node checks, for up to five years.

False negative results

In very few cases, the SLNB may show no evidence of cancer cells, however the melanoma may still come back (less than 2% of all negative SLNBs). This is known as a false negative result. The risk of this occurring is small, however this is one of the reasons why you are kept under clinical follow up following treatment, independent of the results.

Further Information

National Institute for Health and Care Excellence (NICE) (Last Update July 2022). NICE guideline NG14 Melanoma: assessment and management.

If you have access to the internet, you can find this on the NICE website (opens in a new tab).

Surgery admission queries: Plastic surgery admissions coordinator 01223 348658

After surgery queries: Plastic Surgery Unit (PSU) 01223 348509

We are smoke-free

Smoking is not allowed anywhere on the hospital campus. For advice and support in quitting, contact your GP or the free NHS stop smoking helpline on 0800 169 0 169.

Other formats

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Contact us

Cambridge University Hospitals
NHS Foundation Trust
Hills Road, Cambridge

Telephone +44 (0)1223 245151