Dermatopathology quiz: A dome-shaped papule on the cheek

Abstract

The 43-year-old woman was evaluated for a 0.4 cm erythematous, dome shaped papule on her left cheek. Clinically, an irritated or atypical nevus was suspected, and a shave biopsy of the lesion was performed. Histopathological sections revealed a compound, biphasic melanocytic neoplasm composed of both banal appearing nevus cells [Figure 1], and a second population of epithelioid melanocytes forming large dermal aggregates [Figures ​[Figures22 and ​and3].3]. While the conventional component of the neoplasm demonstrated evidence of maturation and dispersion with descent into the dermis, the epithelioid component was monomorphic throughout and showed no evidence of maturation. An Elastic Van Gieson (EVG) stain showed retained elastic fibers within the epithelioid nests. A BRCA1 associated protein-1 (BAP1) immunohistochemical stain mirrored the dichotomous morphology, with nuclear staining in the conventional-appearing nevus cells and the absence of nuclear staining in the epithelioid cells [Figure 4]. Strong p16 staining was noted in the epithelioid component [Figure 5]. Figure 1 A large nodule of epithelioid melanocytes is embedded among small banal nevus cells Figure 2 The epithelioid nodule is sharply circumscribed and the transition between the two populations is abrupt Figure 3 The nuclei of the epithelioid cells are hyperchromatic and pleomorphic. They are unlike the vesicular nuclei with prominent central nucleoli noted in Spitz nevi Figure 4 Nuclear BRCA1 Associated Protein-1 is expressed normally in the banal nevus population, but lost in the epithelioid population Figure 5 The epithelioid cells strongly express p16 The most likely diagnosis is: Malignant melanoma arising in a congenital nevus Epithelioid Spitz nevus Wiesner nevus Metastatic, familial uveal melanoma involving a nevus Balloon-cell change in a congenital nevus. ANSWER: C. Wiesner nevus