Sentinel Lymph Node Biopsy for Melanoma Staging

Lymph fluid drains from your skin in a predictable direction. The sentinel node is the first node along that path — the first place melanoma cells would land if any had left the original site.

To find it, the surgeon injects a small amount of radioactive tracer near the melanoma, usually along with a blue dye. A camera and a handheld probe locate the node or nodes that take up the tracer. Those specific nodes — commonly one to three — are removed through a small incision and examined under a microscope. It is normally done during the same operation as the wide local excision of the melanoma itself.

Thickness drives the conversation. The ASCO and Society of Surgical Oncology guideline puts it this way:

• Thin, non-ulcerated melanoma under 0.8 mm (T1a) — routine sentinel node biopsy is not recommended.
• 0.8 to 1.0 mm, or under 0.8 mm with ulceration (T1b) — may be considered, after a full discussion of benefits and harms.
• Over 1.0 to 4.0 mm (T2 or T3) — recommended.
• Over 4.0 mm (T4) — may be recommended, again after discussion.

Other pathology features — mitotic rate, lymphovascular invasion — and your age and general health can shift the recommendation within those bands.

This is primarily a staging test. It gives the single strongest piece of prognostic information available after the melanoma itself, and it determines whether you are a candidate for adjuvant drug therapy or for clinical trials.

• Negative — no melanoma cells found. Most people fall here. The risk of regional nodes later becoming involved is about 5% or less.
• Positive — melanoma cells were found. This raises the stage and opens the conversation about treatment after surgery.

Be clear about what it is not: removing the sentinel node is not itself expected to cure the melanoma.

For years, a positive sentinel node was followed almost automatically by completion lymph node dissection — removing every remaining node in that basin. The MSLT-II trial tested that assumption. It randomised 1,939 patients with a positive sentinel node to immediate completion dissection or to observation with regular ultrasound of the node basin.

• Three-year melanoma-specific survival was 86% in both groups (P=0.42).
• Disease-free survival was slightly better with dissection (68% versus 63%), driven by better control of disease within the nodes.
• Lymphedema occurred in 24.1% after dissection, versus 6.3% with observation.

In plain terms: taking out all the nodes gave better regional control and more staging detail, but did not help people live longer, and caused roughly four times as much lymphedema.

That result changed practice. Many people with a positive sentinel node are now offered careful observation with scheduled ultrasound of the node basin instead of completion dissection, with dissection kept for higher-risk situations or if nodal disease appears later. The trial did not settle what to do for people who cannot reliably attend frequent follow-up, and that is a legitimate part of the discussion to have openly.

Uncommon but real: a seroma (fluid collection) at the site, numbness or tingling, bruising, wound infection, some risk of lymphedema — lower than after full dissection but not zero — and reactions to the blue dye, which can temporarily tint urine or skin. False negatives happen: the node can be clear while cells have gone elsewhere.

Your pathology report is the document that matters here. Ask for the Breslow thickness, whether the melanoma is ulcerated, and the mitotic rate, and ask how those specific numbers shape the recommendation you are being given. If a sentinel node biopsy is being offered rather than recommended, that wording is deliberate — it means the balance is close enough that your own view of the trade belongs in the decision.

• Completion Dissection or Observation for Sentinel-Node Metastasis in Melanoma (MSLT-II, NEJM 2017)
• MSLT-II full text (PubMed Central)
• NCI — Melanoma Treatment (PDQ®) Patient Version
• American Cancer Society — Tests for Melanoma Skin Cancer