A 1.1 mm melanoma called a dysplastic nevus: staging, margins and ancillary tests
A 58-year-old man from Erbil has a 1.4 cm asymmetric pigmented lesion on his upper back, excised at a district hospital with a 2 mm clinical margin. The outside report calls it 'severe dysplastic nevus, margins clear'. Review at the referral centre shows a superficial spreading melanocytic proliferation with confluent nests, pagetoid scatter and dermal mitoses; Breslow thickness is 1.1 mm, there is no ulceration, the mitotic rate is 2/mm2 and the closest peripheral margin is 0.3 mm. Immunohistochemistry is patchy: Melan-A highlights only the junctional component, SOX10 is strongly positive throughout, HMB-45 is negative in the deep dermal component and PRAME is diffusely positive. The patient is otherwise well and ultrasound shows no suspicious lymph nodes. The surgeon asks whether the original diagnosis was wrong, whether a wider excision and sentinel node biopsy are needed, and whether molecular testing would change management. The patient has travelled from another governorate and wants an answer the same day.
1. State your final diagnosis and pT category, and explain how you reconcile it with the outside report.
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The lesion is an invasive melanoma, superficial spreading type, Breslow 1.1 mm, non-ulcerated, so the AJCC 8th edition category is pT2a (T2a = 1.01–2.00 mm without ulceration). A frequent trap is to assign T1b because the mitotic rate is 2/mm2; since the 8th edition, mitoses are prognostic but no longer part of T staging, and T1b applies only to melanomas <0.8 mm with ulceration or 0.8–1.0 mm regardless of ulceration.
Reconciliation: the outside diagnosis of 'severe dysplastic nevus' is not defensible once dermal mitoses, confluent nests and pagetoid scatter are present in an asymmetric lesion. The outside laboratory may have examined only one level, and a 2 mm clinical margin is not a histological margin. The immunohistochemical pattern (SOX10 strongly positive throughout, diffuse PRAME, loss of HMB-45 in the deep component) is compatible with melanoma, but no stain is a stand-alone diagnostic test: HMB-45 loss can mimic maturation and Melan-A patchiness is common. The diagnosis rests on H&E and should be reported in a synoptic format with Breslow, ulceration, mitotic rate, margins and lymphovascular invasion. Issue a formal report stating the disagreement, retain the slides and blocks, telephone the referring surgeon, and do not silently 'upgrade' the outside report without documented reasoning.
2. What margin and nodal staging do you recommend, and what would you say to a patient who wants to avoid a second operation?
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Margins: for a melanoma of 1.01–2.00 mm, a clinical margin of 1–2 cm is standard; a closest peripheral margin of 0.3 mm is inadequate, so re-excision is required. A 1 cm margin is acceptable at this thickness, and the deep margin should be taken to fascia if it is close or involved. The earlier report's phrase 'margins clear' should not be accepted, because a 0.3 mm margin is not clear for melanoma.
Nodes: at 1.1 mm and non-ulcerated (T2a), sentinel lymph node biopsy should be discussed and offered; ultrasound is useful but is not a substitute for pathology. Reported SLNB positivity for T2 melanoma is roughly 5–10%, and the result changes stage and eligibility for adjuvant therapy and surveillance intensity.
To the patient: her wish to avoid two operations is reasonable and can usually be met by combining wide local excision and SLNB under one anaesthetic, rather than by omitting staging. Explain the false-negative rate, the small risk of lymphoedema and the implications of a positive result, document the consent discussion, and proceed with both. If she declines SLNB, record that decision and arrange close nodal ultrasound follow-up.
3. Would comparative genomic hybridization, FISH or PRAME change your management here, and how do you handle the discrepancy with the outside laboratory?
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No. In this lesion the H&E features are diagnostic, and CGH, FISH (6p25, 11q13, 9p21) and PRAME are adjuncts for ambiguous or spitzoid melanocytic lesions, not confirmatory tests for obvious melanoma. Diffuse PRAME positivity is supportive but not specific, and it cannot convert a nevus into a melanoma by itself. Ordering CGH here would not change the pT category, the 1 cm re-excision or the SLNB discussion; it would only add cost and delay definitive surgery. CGH becomes valuable if the dermal component were borderline or spitzoid and the diagnosis genuinely uncertain.
Discrepancy handling: review the original slides and blocks, issue an amended or consultation report that states the disagreement and the evidence for it, inform the referring clinician by telephone, and send a copy to the outside pathologist. If the outside pathologist disputes the review, seek a second expert opinion rather than allowing two conflicting reports to circulate. Record the episode as a quality issue: melanocytic lesions with dermal mitoses should be referred to a centre with pigmented-lesion experience, and reports should include Breslow, ulceration, mitoses, margins and an explicit statement about SLNB.