An enigmatic disease: childhood Langerhans cell histiocytosis in 2005.

Histiocytic proliferative diseases, although rare, constitute a challenge for pediatric pathologists and hematologists/oncologists because of difficulties in the identification of subtypes and the lack of established standard therapies, resulting in treatment failures, recurrences, or complications. Amongst the different types of such disorders, Langerhans cell histiocytosis (LCH) has been enigmatic to all involved, secondary to a long list of unresolved issues in pathogenesis and treatment. The fundamental dispute over its neoplastic vs. reactive nature remains unsettled. Unique features of LCH, including clonality, cases with spontaneous regression, frequent recurrences, and target tissue/organ tropism, have attracted significant interest. This article reviews the current understanding of LCH in the light of discoveries over the last few decades.