Melanocytic precursors of cutaneous melanoma. Estimated risks and guidelines for management.

There are several recognizable melanocytic precursors of cutaneous melanoma. These precursors include lentigo maligna, dysplastic melanocytic nevi, congenital nevi (of any size), and darkly pigmented lesions of acral surfaces and mucous membranes. Lentigo maligna is an uncommon melanocytic dysplasia, present in 3 per 1000 individuals over the age of 50 years and accounting for 4 percent of all cutaneous melanomas. Dysplastic melanocytic nevi are present in 2 per cent of white adults, and may account for at least a fifth of cases of cutaneous melanoma. Congenital nevomelanocytic nevi are present in 1 per cent of newborns; the vast majority of congenital nevi are smaller than 3 to 4 cm in diameter, while very large congenital nevi are present in 1 in 20,000 to 1 in 500,000 newborns. Very large congenital nevi account for less than 0.1 percent of cutaneous melanomas, whereas small varieties of congenital nevi may account for 15 percent of cutaneous melanomas. If individuals with lentigo maligna live long enough, possibly a third to a half are said to develop melanoma. This figure may be biased high. Persons with dysplastic melanocytic nevi in the familial melanoma setting have an estimated lifetime risk of developing melanoma approaching 100 per cent. Persons with dysplastic melanocytic nevi in other settings may have a lifetime melanoma risk of 18 per cent. Persons with congenital nevi of any size may have a lifetime melanoma risk of at least 5 per cent. Early recognition of these precursor melanocytic tumors, particularly in high-risk individuals (i.e., those with a personal or family history of melanoma), and careful photographic follow-up or prophylactic excision of these lesions may be the most effective means of reducing the morbidity and mortality of cutaneous melanoma. The impact of routine screening and excision of presumed melanoma precursors is unknown. Clinical judgment is required to balance the theoretical risk of melanoma associated with a given precursor and the known risks of surgery and anesthesia for a given individual. It must be kept in mind that the vast majority of acquired melanocytic nevi in adults are harmless. Probably even the majority of dysplastic nevi and small congenital nevi will remain unchanged throughout life. The simple recognition of the existence of melanoma precursors will heighten suspicion for these lesions and raise awareness of the earliest signs of malignant change.(ABSTRACT TRUNCATED AT 400 WORDS)