A distinctive melanocytic lesion associated with melanoma-prone dysplastic naevus syndrome: the hybrid naevus

Abstract

Clinically and histologically, the concept of dysplastic nevi remains controversial. To elaborate more precise criteria for the nevi of patients with dysplastic naevus syndrome (DNS), we examined 58 nevi from seven DNS patients who developed one or several malignant melanomas. Clinical presentation and histomorphology were evaluated, and immunohistochemistry was performed using proliferation marker Ki-S5 and antibody DO-7 to the p53 protein. Sixty nevi from individuals without history of melanoma served as controls. Of the DNS nevi, 21 (36.2%) exhibited no morphological particularities. The remaining 37 nevi presented distinctive histological features consisting of a slight epidermal acanthosis, spitzoid vertically oriented nests of dyscohesive nevus cells, and single-standing atypical melanocytes in the basal cell layer of the epidermis. Immunohistochemical analysis revealed an average proliferation index of 2.5%, which significantly surpassed the mean growth fraction of conventional dysplastic nevi (<1%). No increase in p53 expression was observed. Characteristically, active proliferation was found in junctional single-standing melanocytes with or without nuclear atypia rather than in nest-shaped compounds. In conclusion, certain moles of patients with DNS possess distinctive features. The newly characterized criteria may provide a basis for the diagnosis of DNS and might help to identify patients at increased risk for malignant melanoma by examination of a single biopsy.

Cytological atypia does not equal malignancy: an old but unappreciated truth

“…1A,C). 45,46 Both lesions show various degrees of cellular atypia consisting of atypical nuclei of varying sizes and shapes, nuclear hyperchromasia and prominent nucleoli 46–48 . In our experience, it is by far most often the silhouette of the melanocytic lesion that renders the most important diagnostic feature allowing for a distinction between a severely dysplastic nevus and a melanoma, most importantly circumscription or lack thereof and symmetry or asymmetry 31,49–52 .…”

“…However, they also showed the growth fraction in the familial dysplastic nevi to be consistently less than that observed in the superficial spreading melanoma group, namely 2.5% vs. 6%. Schubert et al's 45 results help illustrate the point that, although histologically worrisome, both sporadic dysplastic nevi and dysplastic nevi from DNS patients stay in the benign proliferative range, whether defined as less than 4% or less than 6%.…”

Melanoma(s) Associated with a Quadrant or Segmental Distribution of Atypical Melanocytic Nevi

“…The first melanoma in our patient had been reported as “spitzoid,” whereas the second showed “Reed nevus‐like” histopathologic features. Moreover, the reexcision specimen showed areas of melanocytic proliferation akin to the so‐called “hybrid” (dysplastic‐spitzoid) nevus, 18 a morphologic marker of risk of melanoma. Finally, the patient had a Spitz nevus excised from her abdomen.…”