Squamous Cell Carcinoma of the Nail Unit: A Comprehensive Review of Clinical Features, Diagnostic Workflow,...

Background/Objectives: Squamous cell carcinoma of the nail unit (SCCNU) is a rare yet often underrecognized malignancy that can lead to delayed diagnosis and significant functional morbidity. This review aims to comprehensively summarize the current understanding of SCCNU, focusing on its clinical, dermoscopic, and molecular features, diagnostic approaches, and evolving management strategies, including the role of emerging technologies and immunotherapy. Methods: A detailed literature review was conducted using peer-reviewed publications, case series, and institutional guidelines related to SCCNU. Emphasis was placed on studies addressing clinical presentation, dermoscopic patterns, molecular pathology, histologic subtypes, imaging, biopsy techniques, staging systems, and both conventional and novel therapeutic approaches. Comparative analyses of histopathological variants and diagnostic algorithms were included. Results: SCCNU presents in patients with diverse clinical manifestations, often mimicking benign nail disorders, leading to diagnostic delays. Dermoscopy improves lesion visualization, revealing features such as vascular changes and onycholysis. Histologically, SCCNU exhibits two main subtypes: basaloid (HPV-related) and keratinizing (HPV-negative) types. Molecular analyses have identified TP53 as the most frequently mutated gene, with additional alterations in HRAS, BRAF, and TERT. Imaging modalities such as MRI and LC-OCT aid in staging and surgical planning. Management is centered on complete excision-often via Mohs micrographic surgery-while topical, intralesional, and HPV-directed therapies are under investigation. Immunohistochemical markers (p16, Ki-67, AE1/AE3) and neoadjuvant immunotherapy represent promising adjuncts. Conclusions: Early diagnosis through non-invasive imaging, improved molecular characterization, and personalized treatment strategies are essential to advancing care in SCCNU. Future directions include clinical trials evaluating immunotherapy, vaccine strategies, and precision-guided surgical approaches to preserve function and minimize recurrence.