Abstract
In this chapter, histopathologic, molecular and biological features are used to group entities in a more taxonomical approach. The most notable changes involve the Spitz tumors. Recent discoveries of molecular events in Spitz tumors—11p and/or HRAS mutations, kinase fusions, and BAP1 inactivation—have forced the creation of this entirely new family of lesions. Identification of specific molecular events in histologically distinct entities (ALK fusion in “plexiform Spitz nevus”, BAP1 inactivation in “halo Spitz nevus”, and HRAS mutation in “desmoplastic Spitz nevus”, for example) has allowed for some terminology consolidation. The pigmented spindle cell nevus (PSCN) has been placed within the family of Spitz tumors to reflect similarities in histology and the discovery of a kinase fusion (involving NTRK3) in PSCN. The controversial pigmented epithelioid melanocytoma has been moved under Dermal Melanocytic Lesions, and nevi with specific site variation (“Special site” nevi) has become its own category. A newly described entity, cutaneous melanocytoma with CRTC1-TRIM11 fusion, has been added. Regarding melanoma, there has been much progress in the areas of pathophysiology, diagnosis, prognosis, and therapy.
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