Suspicious Pigmented Lesion on the Sole
A 58-year-old woman with Fitzpatrick skin type IV presents with a 6-month history of a dark spot on the sole of her right foot. She denies trauma or previous similar lesions. Examination reveals an asymmetric, 12 mm × 8 mm macule with irregular borders and variegated color (brown, black, and grey-blue). Dermoscopy shows a parallel ridge pattern with irregular diffuse pigmentation and areas of regression. She has no personal or family history of melanoma, but she has multiple atypical nevi on the trunk. She is otherwise healthy and takes no medications.
1. What is the most likely diagnosis, and what dermoscopic features support it?
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The most likely diagnosis is acral lentiginous melanoma. The dermoscopic finding of a parallel ridge pattern (pigmentation along the ridges of the skin markings) is highly specific for acral melanoma, as opposed to benign acral nevi which typically show a parallel furrow pattern or lattice-like pattern. Irregular diffuse pigmentation, variegated color, and areas of regression (white scar-like areas) further support malignancy. The ABCD rule is less reliable on acral sites, so dermoscopy is crucial. A biopsy is mandatory for confirmation.
2. How would you proceed with diagnosis and staging?
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An excisional biopsy with 2–3 mm margins is preferred for definitive histopathologic diagnosis and Breslow thickness measurement. If the lesion is too large for primary closure, an incisional biopsy may be done, but it risks sampling error. Histopathology will confirm melanoma and report Breslow thickness, ulceration, mitotic rate, and margins. For staging, sentinel lymph node biopsy (SLNB) is recommended for tumors >0.8 mm Breslow thickness or <0.8 mm with ulceration. Imaging (CT/MRI/PET-CT) is indicated for stage IIB and higher or for symptomatic patients. Genetic testing for BRAF mutations should be considered for potential targeted therapy if advanced.
3. What factors would influence the surgical margins and adjuvant therapy?
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Surgical margins depend on Breslow thickness: in situ: 0.5–1 cm; ≤1 mm: 1 cm; 1.01–2 mm: 1–2 cm; 2.01–4 mm: 2 cm; >4 mm: 2 cm. For acral melanoma, margins are often adjusted to preserve function, but oncologic clearance is priority. Adjuvant therapy is considered for stage III (node-positive) or high-risk stage II. Options include immune checkpoint inhibitors (nivolumab, pembrolizumab) or targeted therapy (dabrafenib + trametinib) for BRAF V600E/K mutated tumors. For stage IV, systemic therapy is guided by mutational status. Regular follow-up with skin and lymph node exams is essential.