A 0.9 mm melanoma with a transected base and a patient who wants it all done in one operation
A 52-year-old woman had a 4 mm shave biopsy of a pigmented lesion on her mid-back six weeks ago. Histology: superficial spreading melanoma, Breslow 0.9 mm, mitotic rate 2/mm², no ulceration, no regression, and the deep margin is involved by melanoma. She is otherwise well, takes no regular medication, and has no family history of melanoma. She has three children aged 12, 15 and 19. She has read about sentinel node biopsy and wants 'everything done at once - I can't take more time off work'; she runs a small catering business and can be off her feet for about 10 days.
1. What operation do you plan and what margin do you take? How does the transected deep margin affect your staging and your plan?
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Plan: wide local excision with a 1 cm clinical margin, down to (but not including) the fascia of the back, with the ellipse oriented along the lines of minimal tension.
- For melanoma ≤1 mm, a 1 cm margin is the accepted standard; 2 cm adds morbidity without proven benefit at this thickness.
- A 0.9 mm Breslow thickness with mitotic rate 2/mm² and no ulceration is T1b, stage IB (assuming clinically node-negative).
- The transected base matters. A shave biopsy that transects the base means the true Breslow thickness may be underestimated: the deepest part of the lesion was left in the patient. Transection does not itself upstage disease, but it does mean the current 0.9 mm is a minimum, not a certainty.
- The re-excision specimen is therefore also the definitive staging specimen. I would ask the pathologist specifically to measure residual tumour and to report the deepest level in the wide excision, and I would tell the patient that the final depth may differ.
- I would not re-biopsy the shave site first - that would simply make the definitive excision harder and delay it.
What would change my plan: if the wide excision shows substantially deeper residual disease (e.g. >1 mm), the margin standard shifts towards 1–2 cm, though re-excising a second time for a 1 cm margin already taken is usually unnecessary; and the indication for sentinel node biopsy becomes stronger.
2. How do you counsel her about sentinel lymph node biopsy, including timing relative to the wide excision, and what the evidence does and does not show? Consider her 10-day work constraint.
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She is a candidate: at 0.9 mm (T1b), sentinel node biopsy should be discussed and offered.
What it gives her
- Accurate nodal staging and prognostic information beyond Breslow thickness and mitotic rate.
- Access to adjuvant therapy and clinical trials if the node is positive; adjuvant options now also exist for high-risk node-negative disease, so staging has become more decision-relevant than it was a decade ago.
What it does not give her
- A proven improvement in melanoma-specific survival from the procedure itself. The large randomised trials showed better staging and disease-free intervals rather than an overall survival benefit, and completion lymph node dissection after a positive node does not improve survival either. I would say this plainly - consent built on an overstated promise is not consent.
- A guarantee of cure if negative; roughly 15–20% of node-negative patients still recur.
Timing - the real judgement call
- Ideally the sentinel node biopsy is done at the same time as the wide local excision, as one anaesthetic and one recovery.
- But her base is transected, so the definitive depth is unknown until the wide excision specimen is reported. Doing both together means committing to a node biopsy based on a potentially under-measured 0.9 mm.
- Practical resolution: because 0.9 mm already crosses the threshold for offering the procedure, and the probability that the true depth falls below the threshold is modest, doing both in one operation is defensible - provided she understands the depth may be revised and that a node biopsy could have been avoidable. The alternative (wide excision first, node biopsy second) is more precise but costs her a second anaesthetic and more time off work.
- I would present both options with the trade-off explicit, and let her decide; either is guideline-compliant.
Fit with her work: a wide excision plus sentinel node biopsy on the back is usually manageable within 10–14 days off her feet for a catering role, particularly if she avoids heavy lifting. I would plan the date around a quiet trading period rather than compromise the operation.
3. She asks whether she should have a PET scan and blood tests, and whether her three children should be genetically tested. Answer both.
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Scans and bloods
- For stage I–II melanoma with a clinically negative node, routine CT or PET-CT is not indicated. The pre-test probability of detectable distant disease is low and the false-positive rate is high, generating anxiety, further imaging and occasionally unnecessary biopsies.
- LDH is not needed for early-stage staging; it is a marker of advanced disease.
- What is indicated is a careful clinical examination of the regional node basin and a skin examination for other lesions, plus education about self-examination of the scar and nodal basins.
- If the sentinel node is positive, staging imaging becomes appropriate at that point.
Genetic testing in the children
- No. A single melanoma with no family history does not meet criteria for germline testing. Testing is generally considered with three or more melanomas (including in situ) in the patient or close relatives, two melanomas with a pancreatic cancer or certain other tumours in the family, or a known familial mutation.
- What the children do need is risk-factor advice, not a blood test: sun protection, avoidance of sunbeds, and prompt review of changing moles - and they should know that having a parent with melanoma is itself a risk factor.
- I would also flag that her own future surveillance is the priority, and that if she develops further primary melanomas the question of genetic referral should be revisited.