ALK‐rearranged histiocytosis: Report of two cases with involvement of the central nervous system

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Abstract
Histiocytoses are a heterogeneous group of localized or disseminated diseases, encompassing diverse clonal proliferative disorders of myeloid dendritic and histiocytic cells. Clinical presentation and patient outcome vary greatly, ranging from mild to life-threatening diseases. Rare cases of histiocytosis harbouring ALK rearrangements, mainly with KIF5B as fusion partner, have been recently reported (1-9), with disease involvement of central nervous system (CNS) described only in occasional cases, as a part of a systemic disease or, exceptionally, as the unique manifestation of the disease.