The Blue Nevus Spectrum: Complexity and Variability of Clinical and Pathological Presentations Mimicking Metastatic Melanoma

ABSTRACT: Blue nevus-related lesions span a broad histopathological continuum, from benign common and cellular blue nevi to atypical cellular blue nevus and malignant blue nevus. The intermediate and malignant forms are rare, diagnostically nonstandardized and may closely mimic metastatic melanoma. We retrospectively reviewed 3 consecutive patients with rare blue nevus variants managed at a tertiary referral center between 2019 and 2025. Cases were eligible if they were histopathologically confirmed, showed diagnostic uncertainty or had initially been interpreted as metastatic melanoma, and had follow-up sufficient to assess clinical outcome. All slides were independently reviewed by 2 dermatopathologists, and 1 case additionally underwent external expert consultation and comparative genomic hybridization. Patient 1 had axillary capsular blue nevi misread as nodal metastases, leading to unnecessary completion dissection. Patient 2 developed malignant blue nevus within a plaque-type blue nevus, with simultaneous benign capsular and vascular-adventitial blue nevus deposits. Patient 3 had amelanotic cellular blue nevus-like melanoma mimicking dermatofibroma, with negative comparative genomic hybridization despite a suspicious subcapsular sentinel-node focus. Integrated clinical, dermatopathological, immunomorphological, and molecular assessment is essential to avoid both under- and over-treatment.