Track: Case Reports

Abstract:

A 69-year-old woman presented with a 6-month history of a progressively enlarging, painful pink nodule on the sole of her right foot. Examination revealed a well-defined exophytic reddish nodule (2.5×3cm) between the second and third toes and palpable right inguinal lymphadenopathy. Biopsy demonstrated abundant atypical melanocytic cells involving the dermis and subcutis (Breslow thickness 2.7 cm), with spindle, epithelioid, and nevoid morphology, and a mitotic rate of 10/mm². Immunohistochemistry was positive for SOX-10, S-100, and Melan-A, and negative for HMB-45, p53, and p63. NRAS exon 3 mutation (p.Q61K) was identified. PET-CT revealed increased FDG uptake in the right inguinal lymph node. A diagnosis of Stage IIIC (T4bN1M0) acral, nodular-type amelanotic melanoma was made. The patient underwent partial right foot amputation with right inguinal and pelvic lymph node dissection; pathology confirmed nodal metastases. She commenced adjuvant immunotherapy with toripalimab and remains under follow-up. Amelanotic melanoma accounts for ~8% of melanomas, with acral involvement being particularly rare. Its lack of pigmentation and atypical clinical features often delay diagnosis. Differential diagnoses for reddish nodules on the foot include pyogenic granuloma, eccrine porocarcinoma, and Merkel cell carcinoma. Histopathology with immunohistochemistry is essential for confirmation, especially when HMB-45 is negative. Early biopsy of chronic, non-healing acral lesions is crucial to avoid diagnostic delay. Surgical excision with appropriate nodal management remains the mainstay, with adjuvant systemic therapy considered in advanced disease.