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Sentinel node biopsy in melanoma: when and why it is offered | CION Cancer Clinics
A sentinel node biopsy is usually offered for melanoma thicker than about 1 mm, or a thinner one with worrying features, when no nodes can be felt or seen on a scan. It finds the first lymph node the melanoma would reach and checks it for cancer cells. The result sets the stage, which guides follow-up and whether medicine after surgery is worth discussing. CION Cancer Clinics’ surgical oncologists in Hyderabad can talk this through with you.
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Medically reviewed by Dr. Muralidhar MuddusettyConsultant Surgical Oncologist · MBBS (AIIMS), MS (Surgery, AIIMS), DNB (Surgical Oncology), MRCS (Edinburgh) · last reviewed September 2026, next review due September 2027
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On this page
- When is a sentinel node biopsy done for melanoma?
- What does the team look at before offering the biopsy?
- What happens on the day of the operation?
- What do the melanoma report words mean?
- What do families believe about this test, and what is true?
- What does the result change, and what can it not tell you?
- Common questions about sentinel node biopsy in melanoma
The short answer
When is a sentinel node biopsy done for melanoma?
A sentinel node biopsy is usually offered when a melanoma is thicker than about 1 mm, or thinner but with features such as ulceration, and no lymph nodes can be felt or seen on a scan. It checks whether melanoma cells have reached the nearest lymph node, a small gland that filters fluid from the skin.
Why the thickness matters
Melanoma spreads first through the lymph channels to the nearest group of nodes. Very thin melanomas rarely do this, so the test would add an operation with little to find. As the melanoma gets thicker, the chance of a node being involved rises, and the result becomes more useful.
What the result is used for
The biopsy does not treat the melanoma on its own. Its main job is to give an accurate stage, which is how far the cancer has gone. That stage decides how closely you are followed up and whether medicines after surgery, such as immunotherapy, are worth discussing.
Who it does not suit
It is not usually offered for very thin melanomas without worrying features, when nodes are already enlarged, or when a person is too unwell for an anaesthetic. It is also less established for melanoma inside the mouth, nose or genital area.
Before it is offered
What does the team look at before offering the biopsy?
Most of this comes from the first biopsy report of the skin lesion. Ask for your own copy.
The depth of the melanoma
Measured under the microscope from the top of the skin to the deepest cancer cell. It is the single strongest guide to whether the node test is worthwhile.
Features on the report
Some findings make node spread more likely even in a thinner melanoma.
Words to look for
- Ulceration, meaning broken skin over the melanoma
- A high mitotic rate, meaning cells dividing quickly
- Cancer cells inside small vessels
Where the melanoma is
On the sole of the foot, the palm or under a nail, a common pattern in India, the drainage is usually predictable. On the head and neck it can drain to more than one place, which makes the test harder.
Your general health
The biopsy needs an anaesthetic. Heart and lung health, other illnesses and what you want from treatment all count in the decision.
It is your choice. You can ask what would change if you did not have it.Not sure whether this applies to you?
Ask an oncologistHow it is done
What happens on the day of the operation?
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The tracer scan
A small amount of a mildly radioactive tracer is injected into the skin around the melanoma scar. A scan then shows which node group it travels to, and the spot is marked on your skin.
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The blue dye
Under anaesthetic, a blue dye may also be injected near the scar. It stains the channels and the sentinel node so the surgeon can see them. Your urine may look blue or green for a day or so.
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Wider removal of the scar
Usually in the same operation, a margin of normal skin around the first biopsy scar is removed. This is called a wide local excision. Some areas need a skin graft or flap to close.
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Finding the node
A small handheld probe picks up the tracer. The surgeon makes a short cut over the node group and removes the node or nodes that are blue or active. Most people go home the same day or the next.
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The report
The node is examined in thin slices with special stains. This takes longer than an ordinary report, so ask when to expect it.
On your report
What do the melanoma report words mean?
- Breslow thickness
- How deep the melanoma goes into the skin, measured in millimetres. This is the depth the team uses to decide on the node biopsy.
- Ulceration
- The skin over the melanoma has broken down, seen under the microscope. It moves a melanoma into a higher stage.
- Lymphoscintigraphy
- The scan after the tracer injection that maps where the lymph from that patch of skin drains.
- Acral melanoma
- Melanoma on the palms, soles or under the nails. It is not linked to sun exposure.
- Micrometastasis
- A very small deposit of melanoma found in the node only under the microscope.
- Adjuvant treatment
- Medicine given after surgery to lower the chance of the melanoma coming back.
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Commonly believed
What do families believe about this test, and what is true?
"Taking out the node will stop the melanoma spreading."
The biopsy is mainly a test. Its value is in telling you and the team the true stage, so that follow-up and any further treatment are planned on facts rather than guesses.
"A black spot on the foot cannot be melanoma, we are not fair-skinned."
Melanoma on the soles, palms and nails occurs in dark skin and is not caused by the sun. It is often found late because people do not expect it. Any changing spot there deserves a biopsy.
"If the node is positive, all the nodes must come out."
Studies in melanoma found that for many people, regular ultrasound checks of the node area did as well as removing all the nodes, with far less leg or arm swelling. Your team will explain which approach fits your report.
"A negative node means nothing more to worry about."
It is good news, and it lowers the stage. It does not remove the need for skin checks and follow-up visits, because the test can occasionally miss a node.
Did you know
The lymph from one patch of skin on the back or the head can drain to more than one group of nodes, sometimes on both sides of the body. The tracer scan is done first so that the surgeon knows every place to look.
Being straight with you
What does the result change, and what can it not tell you?
If the node is clear, follow-up is usually skin checks and visits at set intervals. If it holds melanoma, the stage rises, and the team will discuss closer checks of the node area and whether medicine after surgery is worth considering.
What it cannot tell you
The result does not predict exactly what will happen to you. It is one part of the stage, alongside the thickness, ulceration and scans. A negative node is not a promise the melanoma will stay away, and a positive node does not mean it has already spread elsewhere.
Questions worth asking
How thick was the melanoma, and was it ulcerated? What would the node result change in my plan? Where is the tracer likely to drain? Will the wide excision need a graft? If the node is positive, would you suggest surgery or ultrasound checks? Take a family member to write the answers down.
The decision to have the biopsy belongs to you and your treating team. This page does not advise either way.Questions we are asked
Common questions about sentinel node biopsy in melanoma
Is the tracer injection safe?
The amount of radioactivity is very small and fades quickly. It is widely used for this purpose. The injection into the skin can sting for a short while. Tell the team if you are pregnant or breastfeeding, because the plan may be changed.
Will I be admitted to hospital?
Many people go home the same day or the next morning. A longer stay is more likely if a skin graft or flap was needed to close the wide excision, or if nodes in the groin were removed. Ask your surgeon what to plan for before the day.
Why does my skin or urine look blue?
The blue dye used to find the node passes out through the urine, which can look blue or green for a day or two. The skin near the injection can stay faintly blue for weeks or longer. This is expected. Tell the team at once if you feel breathless or develop a rash.
Can the melanoma on my foot drain to my groin?
Yes. Lymph from the foot usually drains to the groin, and sometimes to the node behind the knee. The tracer scan shows which applies to you before the operation, so the surgeon knows exactly where to make the cut.
What problems can happen after the biopsy?
The common ones are bruising, a collection of fluid under the cut, and wound infection. Some swelling of the arm or leg can happen, though it is much less common than after removing all the nodes. Report redness, fever or a rapidly swelling wound to your team.
My melanoma was already removed. Is it too late?
Usually not. The biopsy is normally planned after the first diagnostic removal, often together with the wider excision of the scar. Bring the original report and slides so the team can confirm the thickness before deciding. Delay is worth avoiding, so do not wait for the scar to fade.
Do I need a PET-CT scan before this?
Not always. For many early melanomas, scans add little before the node biopsy. Scans are more often used for thicker melanomas, when the node is positive, or when symptoms suggest spread. Your team will decide which tests suit your stage.
Does insurance or Aarogyasri cover it?
Cancer surgery for melanoma, including the node biopsy, is often covered when it is part of an approved treatment plan at an empanelled hospital. Aarogyasri, CGHS, ECHS, EHS and cashless insurance all have their own rules. Call the helpline with your card details before admission.
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Sources
- NICE — Melanoma: assessment and management (NG14)
- National Cancer Institute — Melanoma Treatment (PDQ) - Patient Version
- American Cancer Society — Surgery for Melanoma Skin Cancer
- Cancer Research UK — Melanoma
- National Cancer Institute — Sentinel Lymph Node Biopsy
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Keep reading
Related pages
Sentinel Node Positive: Do All the Nodes Come Out?What happens if the melanoma node holds cancerThe Blue Dye and Radioactive Tracer ExplainedHow the node is found on the dayLymphoedema Risk: Sentinel Node vs Full ClearanceThe swelling risk in the arm or legImmunotherapy guideMedicine after surgery for higher-stage melanoma
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