Histopathology and Clinical Features of SPARK Nevi in a Multi-Institutional Cohort.

Abstract

Background/ObjectivesSpitz nevus with architectural features of a Clark/dysplastic nevus ("SPARK nevus") is an uncommon melanocytic lesion closely mimicking dysplastic nevus and melanoma, creating diagnostic challenges. This study aimed to delineate the clinical, histopathologic, and immunohistochemical features of SPARK-pattern lesions and to clarify their biologic behavior.MethodsA multi-institutional retrospective study across six academic centers identified 74 SPARK nevi. Candidate lesions were re-reviewed at each institution by board-certified dermatopathologists using predefined inclusion criteria requiring concurrent Spitzoid cytology and Clark-type architectural features. The demographic, clinical, histologic, immunohistochemical, and follow-up data were collected and reviewed.ResultsThe cohort showed a predominance of female patients (76%) with a mean age of 32.4 years (range 11-68), and lesions were small (mean diameter 5.8 mm, range 2-20 mm), most often on the proximal extremities and trunk. Histologically, lesions were mainly compound (70%) with Spitzoid cytology in Clark-type architecture; cytomorphology was mixed epithelioid-spindled (47%) or epithelioid (41%), Kamino bodies were infrequent (9%), inflammation was usually non-brisk (62%), and cytologic atypia often reached moderate to severe grades. Immunohistochemistry (performed in 55%) showed PRAME negativity, retained p16, and low MKI67 indices, and follow-up (available in 93%; median 18 months) revealed one local recurrence, two metachronous SPARK nevi, and no SPARK-related deaths.ConclusionsThis largest series defines the clinicopathologic and immunohistochemical spectrum of SPARK-pattern lesions and demonstrates overall benign behavior despite morphologic overlap with dysplastic nevi and melanoma. SPARK is most appropriately interpreted as a morphologic pattern encompassing lesions arising from multiple melanocytic pathways.