Acral pigmented lesion with a misleading punch biopsy
A 54-year-old man with Fitzpatrick type IV skin presents with an enlarging pigmented lesion on the right sole that he first noticed 8 months ago. It is now 14 mm across, with irregular borders and variegated brown, black and grey colour. There is no bleeding or ulceration. He has no family history of melanoma and no history of sunburn. Dermatoscopy shows a parallel ridge pattern, irregular diffuse pigmentation and a blue-white veil. A colleague performed a 4-mm punch biopsy at the periphery 3 weeks ago; histopathology reported “benign junctional naevus with mild atypia”. The lesion has continued to enlarge. He asks whether he can have a simple shave excision because he cannot afford time off work.
1. What is your interpretation of the dermatoscopy and the prior biopsy? What procedure do you perform now?
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The dermatoscopic parallel ridge pattern is highly specific for acral melanoma; pigment follows the ridges rather than the furrows. Irregular diffuse pigmentation and a blue-white veil add to the concern. The prior 4-mm punch was taken at the periphery, which is a common source of sampling error because acral melanomas are heterogeneous and may have a benign-looking edge. A report of benign junctional naevus does not exclude melanoma when the clinical and dermatoscopic findings are discordant.
I would perform a complete excision biopsy with a narrow margin of 2–3 mm and full-thickness removal down to fat, oriented for the pathologist. A shave excision is inappropriate because it does not allow accurate Breslow thickness measurement and may transect the lesion. I would request immunohistochemistry with S100, Melan-A, HMB-45 and SOX10 if the morphology is ambiguous. The patient should be told that the previous biopsy was not adequate and that the new procedure is diagnostic, not cosmetic.
2. Assuming the excision shows invasive melanoma, how do you decide margins and sentinel node biopsy?
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Margins depend on Breslow thickness and, for thin lesions, ulceration. For melanoma in situ, a 0.5 cm margin is adequate. For invasive melanoma up to 1 mm, a 1 cm margin is standard; for 1–2 mm, a 1–2 cm margin; and for greater than 2 mm, a 2 cm margin. Acral location can make a 2 cm margin functionally difficult, but the oncological margin should not be compromised without multidisciplinary discussion.
Sentinel lymph node biopsy is generally discussed for tumours greater than 0.8 mm, or 0.8–1.0 mm with ulceration, and for thicker tumours. It is not indicated for melanoma in situ. The decision should incorporate Breslow thickness, ulceration, mitotic rate, patient preference, and access to reliable sentinel node services. If the sentinel node is positive, the patient should be referred for staging and consideration of systemic therapy or a clinical trial. I would also check baseline imaging according to stage.
3. What do you tell him about work, prognosis, and the request for a shave?
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I would explain that a shave excision is not safe for a lesion that may be melanoma because it prevents accurate measurement of invasion and may leave tumour behind. A complete excision biopsy can usually be done under local anaesthetic, and the initial procedure may require only a short period away from work; a subsequent wide local excision may require 1–2 weeks of modified activity depending on the site. The need for time off work is not a reason to compromise diagnosis.
Prognosis is determined by stage, especially Breslow thickness, ulceration, and sentinel node status. Acral melanoma is often diagnosed later than truncal melanoma, so prompt complete excision matters. I would avoid giving a precise prognosis before the excision histology is available. I would also explain that acral melanoma is not caused by sun exposure in the same way as melanoma on sun-exposed skin, so he should not blame himself, but he should protect the feet from trauma and inspect the soles periodically.