Longitudinal melanonychia as a presenting sign of nail unit squamous cell carcinoma: A case series and narrative review

Background: Nail unit squamous cell carcinoma (nSCC) presenting as longitudinal melanonychia is underrecognized, particularly among patients with skin of color (SOC). This review identifies patient, tumor, and human papillomavirus (HPV) characteristics. Summary: A review from peer-reviewed articles plus five institutional cases yielded 59 total cases. The majority (69.6%) were male, with a median age of 53 years. Among those with known Fitzpatrick Skin Type or race, 86.9% had SOC. Fingernails accounted for 87.7% of tumors. Longitudinal melanonychia was the only finding in 23.7% of cases, while hyperkeratosis, onychodystrophy, and verrucous changes were reported in 30.5%, 18.6%, and 15.3% of cases, respectively. The lateral nailfold was involved in 80.6% of cases. Most (81.4%) tumors were in situ at diagnosis. When performed, HPV testing was positive in 76.0% of cases, with high‑risk types (including HPV 16, 56, 58, and 59) predominating (76.9%). Key Messages: nSCC should be considered in the differential of longitudinal melanonychia, especially in patients with SOC over age 40 and a history of HPV infection presenting with lateral nailfold involvement, hyperkeratosis, onychodystrophy, or verrucous changes. Recognizing these findings may reduce diagnostic delay and allow earlier, tissue‑sparing treatment.