Histopathology of nail unit tumours: diagnostic features and emerging advances.

Nail unit tumours are unusual and frequently underrecognized neoplasms that may pose diagnostic challenges to both clinicians and dermatopathologists. This review focuses on nail unit tumours that most frequently present diagnostic difficulty, owing to significant clinical or histopathological overlap with one another, and provides a comprehensive update on their histopathology. Entities covered include melanocytic tumours, onychopapilloma, onychomatricoma, superficial acral fibromyxoma, onychocytic matricoma, onychocytic carcinoma, subungual keratoacanthoma, squamous cell carcinoma and onycholemmal carcinoma. For each entity, we summarize the clinical presentation, histopathological features, immunohistochemical profile and relevant updates in classification and molecular pathogenesis. Familiarity with this diverse group of neoplasms is essential for timely and accurate diagnosis, given the significant diagnostic delay that commonly affects patients with nail unit tumours.