Blue nevus, malignant
Malignant blue nevus is a rare melanoma
that develops in a pre-existing dermal melanocytosis, most frequently a benign blue nevus
. The tumour consists of two components: the benign component of the pre-existing lesion and a malignant component, which typically appears as a deep-seated expansile nodule involving the reticular dermis and subcutaneous fat, but may also involve the superficial dermis and ulcerate the epidermis. The neoplastic melanocytes are large spindled to epithelioid cells which usually contain little or no melanin. The malignant component is often associated with a perivascular inflammatory infiltrate (mainly lymphocytes).
The transition from a benign to the malignant lesion is usually abrupt. Malignant blue nevus arises most frequently on the scalp, face and orbit; other commonly affected sites are back, buttocks, extremities, hands, and feet. The tumour typically presents as a black nodule which may range in diameter from 0.5 to 8 cm (mean: 2.1 cm).
Melanoma associated with blue naevus is exceedingly rare. It affects predominately Caucasians and may occur in all age groups (mean age at diagnosis 44 years). It is a highly aggressive tumour that frequently metastasizes to regional lymph nodes (31% of reported cases) and distant sites (42%), most frequently to liver, followed by lung, brain, skin and bone. The prognosis is poor
LeBoit PE, Burg G, Weedon D, Sarasin A (Eds.)
World Health Organization Classification of Tumours. Pathology and Genetics of Skin Tumours
IARC Press: Lyon 2005