Clinical Characteristics of Nail Unit Melanoma in Türkiye: The Experience of Two Tertiary Dermatology Centers.

Background: The literature on the clinical presentations of nail unit melanoma (NUM) in different countries is limited. Aims: To assess the specific clinical characteristics of NUM in Türkiye. Study Design: A retrospective cross sectional study. Methods: Patients with NUM in two centers were retrospectively evaluated for their clinicopathological features, including the location, laterality, destruction of the nail plate, erosion or ulceration, presence of longitudinal melanonychia (LM), Hutchinson's sign (HS), and the absence of pigmentation and Breslow thickness. These variables were compared in terms of the main location of the NUMs (fingernail versus toenail). Results: A total of 37 patients (54.1% female) of mean age 61.9 ± 14.8 years were enrolled. In most cases, NUMs were located in the fingernails (62.2%), with the most common location being the thumbnails (45.9%), followed by the big toenails (32.4%). Five cases had in situ melanoma presenting with LM. The mean Breslow thickness of invasive NUM lesions (n = 26) was 4.7 ± 4.1 mm (median: 3). Although all in situ NUMs were located on the hands, no statistically significant difference was noted in the Breslow thickness of invasive NUMs on the toenails and fingernails. NUMs were hypomelanotic/amelanotic in 10 (27%) patients. LM was clinically evident in 40.5% of the patients and was significantly more frequently observed on fingernails. The HS of the nail folds was noted in 40.5% of the patients, with the proximal (73.3%) and distal (73.3%) nail folds being most commonly involved. Total or partial destruction of the nail plate was recorded in 24.3% and 51.4% of the patients, respectively. Erosion and/or ulceration on the surface of the NUM was clinically present in most (75.7%) cases. Invasive NUMs associated with LM (n = 10) displayed partial destruction of the nail plate (n = 9), erosion and/or ulceration on the tumor surface (n = 7), and HS (n = 6). Conclusion: The clinical characteristics of patients with NUM, such as more common localization on the hands, a high rate of preference for thumbnail and big toe, and the ratio of HS, were similar to the studies reported from diverse countries. Partial destruction of the nail plate is an important clinical feature of NUM. Furthermore, LM is more frequently observed in NUMs on the fingernails.