Nevi and Melanoma

Abstract

Cutaneous melanoma is an aggressive form of skin cancer derived from skin melanocytes and is associated with significant morbidity and mortality. A significant fraction of melanomas are associated with precursor lesions, benign clonal proliferations of melanocytes called nevi. Nevi can be either congenital or acquired later in life. Identical oncogenic driver mutations are found in benign nevi and melanoma. While much progress has been made in our understanding of nevus formation and the molecular steps required for transformation of nevi into melanoma, the clinical diagnosis of benign versus malignant lesions remains challenging.

Keywords: Atypical nevus; Dysplastic nevus; Melanoma; Nevus; Senescence.

Figure 1.

Clinical and histologic appearance of nevi. A) Clinical photograph of patient with high density of nevi, including nevi with clinical atypia. B) Histological appearance of a junctional nevus, showing nested proliferation of melanocytes. From Drozdowski et al. Dysplastic nevus part I: Historical perspective, classification, and epidemiology. J Am Acad Dermatol 88(1):1–10 (Elsevier).(A)

Figure 2.

Classes of melanocytic nevi. In addition to common acquired nevi, several distinct types of nevi have been identified A) Blue nevus. Note that his lesion is macular and that the the blue/gray color is due to deep dermal infiltration of nevus melanocytes B) Spitz nevus on the finger of a 5-year-old child. These lesions often present a diagnostic and therapeutic challenge.

Figure 3.

Melanoma may be derived from nevus precursor or form de novo. A) BRAF^V600E mutation leads for melanocyte proliferation followed by oncogene-induced senescence, resulting in formation of a benign nevus. At low frequency, nevi transform to melanoma. B) A significant fraction of melanomas form in the absence of a nevus precursor. It has been hypothesized that highly mutated epidermal melanocytes are at high risk for melanoma transformation following BRAF^V600E mutation. From Baykal et al. The spectrum of benign dermal dendritic melanocytic proliferations. J Eur Acad Dermatol Venereol, 3(6):1029–1041 (A)Brown et al. Spitz Nevus: Review and Update. Clin Plast Surg (4):677–686 (B)