Asymmetric pigmented lesion on the sole

Acral lentiginous melanoma, Breslow 1.9 mm, ulcerated (pT2b), SLN-positive (pN1a) — AJCC Stage IIIB — treated by wide local excision, SLNB and adjuvant pembrolizumab

Learning points

• Acral lentiginous melanoma (ALM) is proportionally commoner in Fitzpatrick IV–VI skin and is a recognised equity gap in UK skin cancer practice; diagnostic delay is well documented. Have a low threshold for biopsy of any new or changing plantar / palmar / digital lesion in skin of colour.
• Parallel ridge pattern on dermoscopy (Saida) — pigment on the raised ridges rather than the furrows of acral skin — is a high-specificity sign in trained hands; the original series reported sensitivity in the mid-80% range and specificity ~99% for early acral melanoma.
• Acral melanoma is histologically often lentiginous with deep dermal invasion at presentation due to diagnostic delay; ulceration is common. Despite the histological subtype, AJCC 8 staging and NICE NG14 margins apply uniformly.
• SLNB threshold: NG14 says not to offer SLNB for stage IA, but to consider it for Breslow 0.8–1.0 mm melanoma with adverse features and for Breslow >1.0 mm after shared discussion — a 1.9 mm ulcerated melanoma is firmly in the group where SLNB should be discussed.
• Plantar reconstruction principles: choose tissue suitable for weight-bearing (full-thickness graft, medial plantar artery flap, dermal substitutes). Avoid skin grafts in weight-bearing zones unless underlying soft tissue is adequate.
• Adjuvant anti-PD-1 is NICE-approved for completely resected stage IIB–III melanoma — pembrolizumab for stage IIB / IIC (NICE TA837) and stage III (NICE TA766); nivolumab for stage III / IV (NICE TA684). ALM tends to respond less well to checkpoint inhibitors than UV-driven melanoma because of lower tumour mutation burden, but adjuvant ICI still has measurable benefit.
• Macroscopic vs microscopic stage III matters for the neoadjuvant pathway. From 28 April 2026, NHS England (URN 2426) routinely commissions neoadjuvant followed by adjuvant pembrolizumab for macroscopic resectable stage IIIB–D melanoma (palpable nodes, radiologically visible nodes, or in-transit / satellite metastases), age ≥ 12. This case had a sub-capsular SLN deposit < 1 mm detected on SLNB — microscopic nodal disease — which is explicitly excluded from URN 2426. The correct pathway here is therefore adjuvant pembrolizumab (TA766) or adjuvant nivolumab (TA684) alone, not the neoadjuvant regimen. The distinction matters because it changes the timing of systemic therapy relative to surgery, the consent conversation, and the dose schedule.
• BRAF mutation testing remains routine even in ALM because of the small (~10–15%) BRAF-mutant subset eligible for targeted therapy.