Sentinel lymph node

What “sentinel” means

Lymph from the melanoma area reaches one or more first-draining lymph nodes, called sentinel nodes. Biopsy involves locating and removing them to look for tumour cells under the microscope. It is not the same as clearing the whole lymph node basin and does not remove the melanoma in the skin, which requires a separate procedure.

Its main role is staging and prognosis: it helps distinguish disease with no detected nodal metastases from disease with small regional deposits. This information may change follow-up planning and discussions about subsequent treatment. However, biopsy should not be presented as a guarantee of cure or improved survival for every patient.

The likelihood of a positive result varies with the melanoma’s features. Historical percentages linked only to thresholds such as 1.5 or 4 mm do not reliably describe an individual’s risk: the complete pathology report and clinical assessment are more useful than an isolated number.

Sources for this section: National Cancer Institute — Melanoma Treatment (PDQ), health professional version; EANM — Practice guidelines for lymphoscintigraphy and sentinel lymph node biopsy (2015).

When it is offered

According to ESMO, biopsy is not routinely recommended for pT1a melanomas, meaning less than 0.8 mm thick without ulceration. It should be discussed for pT1b tumours: 0.8–1.0 mm thick, or thinner than 0.8 mm with ulceration. For melanomas over 1.0 mm without clinically involved nodes, it is recommended for staging. Special circumstances, such as thickness that cannot be reliably determined, require individual discussion.

These thresholds guide the consultation rather than automatically deciding surgery for everyone. The specialist considers general health, how the result would affect subsequent decisions, procedural risks and personal preferences. Melanoma in situ does not ordinarily require sentinel node biopsy.

If a node is already clinically suspicious, targeted diagnostic assessment is needed: sentinel biopsy is not used to bypass evaluation of a possible evident metastasis. Likewise, CT or PET is not an indiscriminate prerequisite for every sentinel biopsy: imaging requirements depend on stage, signs and symptoms.

Sources for this section: ESMO — Cutaneous melanoma: Clinical Practice Guideline (2024/2025); NICE NG14 — Melanoma: assessment and management, recommendations.

How the nodes are located

Nuclear medicine uses a tracer, usually labelled with technetium-99m, injected into the skin near the melanoma site. Lymphoscintigraphy shows the drainage pathways; during surgery a gamma probe helps the surgeon locate the identified nodes. Some protocols also use a dye. The team explains timing, preparation and individual precautions.

There may be several sentinel nodes and more than one drainage basin, particularly for the trunk or head and neck. Selecting only the closest node or the strongest signal is insufficient: the drainage map matters. SPECT/CT may add anatomical information in appropriate cases without making the procedure infallible.

Planning is coordinated with wide excision of the melanoma. Ask whether the procedures will take place during the same operation and which incisions are expected: node-biopsy scars may be some distance from the primary tumour scar. Their location does not mean metastases have already been found.

Sources for this section: EANM — Practice guidelines for lymphoscintigraphy and sentinel lymph node biopsy (2015); Mayo Clinic — Video: sentinel node biopsy for melanoma.

Pathology and timing of the result

A pathologist examines the material. Detecting small deposits requires careful assessment of the tissue with appropriate sections and stains; immunohistochemistry can help identify melanocytic cells. Markers such as S100 or HMB45 should not be interpreted in isolation: diagnosis depends on the combined findings.

Patients should not automatically expect an answer during surgery followed by immediate completion dissection. The definitive result is communicated according to laboratory timing and discussed in context. Specialist review may be useful if the report is uncertain.

Molecular techniques mentioned in historical literature, such as detection of melanocyte-associated transcripts, should not be presented as mandatory tests or replacements for histology. A more sensitive test is not automatically more useful for clinical decisions: it matters what the test detects and how the result changes care.

Sources for this section: EANM — Practice guidelines for lymphoscintigraphy and sentinel lymph node biopsy (2015); Faries et al. — MSLT-II, NEJM (2017).

Negative or positive result: what changes

A negative result means that no metastases were identified in the sampled nodes using the techniques applied. This is favourable information, but it does not exclude every possible recurrence or future spread. Follow-up remains necessary and is based on the whole clinical picture, not the sentinel result alone.

A positive result documents regional involvement; it does not by itself establish distant metastases. The case is reassessed for staging, basin surveillance and possible adjuvant therapies. Complete dissection is no longer the automatic consequence: structured ultrasound surveillance is central for many patients, while exceptions require multidisciplinary discussion.

Ask who will arrange the scans, on what schedule and what to do if a lump appears. “Observation” does not mean absence of care. If follow-up cannot realistically be performed, that difficulty should be made explicit when choosing the pathway.

Sources for this section: NICE NG14 — Melanoma: assessment and management, recommendations; Faries et al. — MSLT-II, NEJM (2017).

Risks, limitations and useful questions

Like any operation, biopsy may cause pain, bleeding, infection or fluid accumulation; altered sensation and lymphoedema are possible. Dye can cause allergic reactions or persistent staining. Risk depends on the site, procedure and individual circumstances: a single percentage does not describe every patient.

A false-negative result is possible: the test may miss existing disease or cannot predict everything that will become apparent later. Drainage complexity and team experience matter. The result must therefore be integrated with examination, the primary melanoma report and follow-up.

Before deciding, ask what likelihood of a positive result the team estimates, how care would change after either result and which risks are most relevant to you. After surgery, follow wound-care instructions and contact the service if problems arise, without waiting for a scheduled visit when discharge instructions identify urgent warning signs.

Sources for this section: Mayo Clinic — Sentinel node biopsy.

Research and historical material

Selective lymphatic mapping in melanoma is associated with Morton and colleagues’ work, published in 1992. The technique helped distinguish targeted assessment of first-draining nodes from systematic lymph node clearance. Current decisions, however, also rely on subsequent trials and guidelines.

Research aims to make staging and surgery more proportionate to risk. Strategies guided by immunotherapy response, such as those studied in PRADO, concern specific settings and do not justify independently omitting sentinel biopsy. The parent page discusses experimental treatments and their limitations.

The book covers retained below document the history of this topic in the site archive. They are neither current guidelines nor purchase recommendations. Mayo Clinic’s educational video can also help explain the procedure, alongside explanations from your own team.

The Sentinel Lymph Node Concept — historical cover retained in the archive; not a current guideline.

Sentinel Lymph Node Biopsy — historical cover retained in the archive; not a commercial recommendation.

Sources for this section: Hoeijmakers et al. — PRADO, 5-year follow-up, Nature Medicine (2026); Mayo Clinic — Video: sentinel node biopsy for melanoma; Morton et al. — Technical details of intraoperative lymphatic mapping (1992).

Sources and update

Editorial revision and source consultation: 17 October 2026. Study dates distinguish current evidence from historical documents. This date does not certify specialist clinical review.