Verrucous naevoid and keratotic malignant melanoma: a clinico-pathological study of 20 cases

Verrucous naevoid malignant melanoma is a recently described variant of malignant melanoma that may be confused both clinically and histologically with benign lesions. This study reports the clinical and pathological features of 20 such cases. These constituted 3.2% of all melanomas diagnosed in the Department of Pathology, Aberdeen University, in the period 1970-1991. They occurred more often on the back and limbs of male patients with a mean age of 57 years. Clinical diagnosis of benign lesions (warty naevi, papillomas, seborrhoeic keratosis and cysts) were made in over 50% of the cases. Eight patients had metastases, seven of whom died of their disease. Microscopically, these lesions exhibited a spectrum of naevoid features such as symmetry, exophytic and papilliferous growth pattern, hyperkeratosis and pseudo-epitheliomatous hyperplasia. The majority, however, showed lateral intra-epidermal spread and were composed of large epithelioid cells exhibiting various degrees of cellular pleomorphism. Histological classification was difficult, as more than 50% of the cases were initially labelled unclassifiable. The marked papilliferous architecture of these lesions made assessment of Breslow depth and Clark levels difficult. Initially, 10% of the cases were histologically diagnosed as benign. It is therefore important for surgical pathologists to recognize this unusual variant of malignant melanoma, as it may be confused both clinically and pathologically with benign lesions.