# Dermoscopy of Subungual Squamous Cell Carcinoma: A Systematic Review

## TL;DR

This study reviews how close-up nail imaging can help identify a rare nail cancer, improving early diagnosis and treatment.

## Contribution

The study systematically identifies dermoscopic features that distinguish invasive and in situ subungual squamous cell carcinoma from benign conditions.

## Key findings

- Invasive subungual squamous cell carcinoma commonly shows subungual hyperkeratosis, onycholysis, irregular borders, and splinter hemorrhages.
- In situ lesions more often present with melanonychia and lower rates of hyperkeratosis.
- Dermoscopy can help differentiate cancer from benign conditions like warts and onychomycosis.

## Abstract

Subungual squamous cell carcinoma is a rare cancer that starts beneath a fingernail or toenail and is often mistaken for common, harmless nail problems, which can delay in correct treatment by years. We reviewed published reports to find which visual signs, seen with a close-up nail imaging technique that reveals fine patterns not visible to the naked eye, most reliably indicate this cancer. We analyzed 20 studies describing 121 confirmed cases. Tumors that had already grown into surrounding tissue most often showed a firm, thick build-up under the nail, lifting of the nail plate, irregular edges of the lesion, and small blood spots. Early, noninvasive cancer confined to the surface more often appeared as a single dark streak of pigment. These findings mean that careful use of close-up nail imaging can help doctors decide when to perform a biopsy sooner, reducing delays in diagnosis and treatment, preserving nail and bone health, and improving patients’ long-term outcomes.

Introduction: Subungual squamous cell carcinoma is a rare malignancy of the nail unit that is frequently misdiagnosed as benign nail disease, leading to prolonged diagnostic delays and sometimes invasive spread. Objective: To synthesize the dermoscopic features of histologically confirmed subungual squamous cell carcinoma and to compare patterns between invasive and in situ disease. Methods: We performed a systematic review and meta-analysis (PROSPERO CRD42023470387) following PRISMA and MOOSE guidance. PubMed, Scopus and Cochrane CENTRAL were searched. Extracted data included study design, lesion counts, histologic subtype and specific dermoscopic signs. Random-effects meta-analysis (DerSimonian–Laird with Freeman–Tukey transformation) produced pooled prevalences with 95% confidence intervals. Between-study heterogeneity was assessed with Cochran’s Q and I2. We used subgroup and meta-regression analyses to explore the influence of histologic subtype, sample size and publication year. When the data allowed, diagnostic odds ratios were calculated versus common benign mimickers. Results: Twenty studies comprising 121 lesions (96 invasive, 25 in situ) were included. In invasive lesions, the most common dermoscopic findings were subungual hyperkeratosis (pooled prevalence 89%; 95% CI 78–97; I2 = 0%), onycholysis (85%; 75–93; I2 = 28%), irregular borders (72%; 50–90; I2 = 42%), and splinter hemorrhages (52%; 40–65; I2 = 36%). In situ lesions more often presented with melanonychia (89%) and showed lower rates of hyperkeratosis (50%). Meta-regression identified histologic subtype as a significant predictor of feature prevalence (p < 0.01). Key comparative performance estimates included a diagnostic odds ratio of 12.6 (95% CI 8.3–19.1) for polymorphous vessels distinguishing squamous cell carcinoma from warts and 6.8 (95% CI 3.2–14.5) for hyperkeratosis versus onychomycosis. Conclusions: Dermoscopy reliably identifies features, particularly hyperkeratosis, onycholysis, irregular margins and hemorrhagic spots, that are common in invasive subungual squamous cell carcinoma; in situ disease more commonly presents with pigmentary changes. Recognition of these signs should lower the threshold for biopsy of suspicious single-digit nail lesions and may facilitate earlier diagnosis and treatment.