ABSTRACT
Malignant nail tumors are rare with Bowen disease plus squamous cell carcinoma and melanoma being by far the most frequent. Onychocytic and onycholemmal carcinomas were only recently described and are very rare. Bowen disease is an in situ carcinoma with histological features of human papillomavirus histogenesis. It may progress to invasive squamous cell carcinoma, but non-HPV-related squamous cell carcinoma also occurs though much less frequently. A variant is carcinoma cuniculatum. Aggressive digital papillary adenocarcinoma is rare but has a poor prognosis. All other carcinomas are exceptional as are malignant fibrous tumors. Kaposi sarcoma is occasionally seen to involve the nail unit. Only very few Merkel cell carcinomas were observed around the nail. Clinically non-specific nail alterations may occur in Langerhans cell histiocytosis. Malignant T-cell lymphomas, particularly generalized mycosis fungoides and Sézary syndrome, cause a non-specific nail dystrophy. The most serious nail tumor is ungual melanoma. Approximately three quarters of them start with a longitudinal melanonychia, which stands out by irregular brown lines and asymmetry. The diagnosis is particularly difficult in dark-skinned individuals. Whereas histopathology is unequivocal in advanced cases it may be very delicate in early melanoma. Metastases to the distal digit are rare and often show an enormous swelling with discoloration and surprisingly little pain.
