Current Concepts in Histiocytic Neoplasms

Histiocytic neoplasms are a diverse group of disorders arising from macrophages, dendritic cells, and monocytes of the mononuclear phagocyte system. These neoplasms encompass a clinical spectrum from indolent, self-limited, and localized conditions to highly aggressive malignancies. Since the publication of the Revised Fourth Edition of the World Health Organization (WHO) classification, advances in molecular diagnostics have improved our understanding of the pathogenesis and classification of these disorders. In contrast to the Revised Fourth Edition, the International Consensus Classification (ICC) now recognizes Rosai-Dorfman-Destombes disease as a neoplastic disorder and introduces ALK-positive histiocytosis as a distinct entity. This manuscript reviews the current concepts regarding histiocytic neoplasms, focusing on the diagnostic criteria recommended by the ICC based on histopathology, immunophenotype, molecular alterations, as well as clinical and imaging characteristics.