The xanthogranuloma family of histiocytic neoplasms in the molecular era: Erdheim-Chester disease and beyond

Histiocytic neoplasms with xanthogranulomatous morphology encompass a continuum of disorders-from isolated cutaneous juvenile xanthogranuloma (JXG) or adult xanthogranuloma (AXG) to the multisystem Erdheim-Chester disease (ECD)-that share overlapping histopathologic and molecular features. In this article, we (1) define the spectrum of xanthogranuloma lesions, highlighting morphologic and immunohistochemical commonalities; (2) examine the clinical and radiographic criteria that distinguish localized juvenile xanthogranuloma/adult xanthogranuloma from classical Erdheim-Chester disease and related entities; (3) review the latest insights into MAPK pathway alterations that blur traditional diagnostic boundaries; and (4) outline contemporary management strategies, including approaches to staging "occult" disease, patient selection for BRAF and MEK inhibitors, and the role of other targeted and nontargeted agents. Readers will gain practical frameworks for recognizing early or atypical presentations, integrating molecular testing into routine practice, and optimizing personalized therapy across the xanthogranuloma family.