Cladribine (2-chlorodeoxyadenosine) is metabolised and phosphorylated in a cell up to 2-chloroadenosine triphosphate which is the actual effective form of the drug. The greatest accumulation of 2-chloroadenosine triphosphate is in the most active cells, where activating (phosphorylation) enzyme, deoxycytidine kinase, has the highest activity, whereas inactivating enzyme (dephosphorylation), cytoplasmic 5-nucleotidase, has the lowest activity. A very good ratio of the both enzymes for high effectiveness of cladribine is in resting and proliferating lymphocytes. Therefore, cladribine is an effective medication for hairy cell leukemia, Waldenström macroglo-bulinemia but also for chronic -B-lymphocytic leukemia. However, such high concentrations of 2-chloroadenosine triphosphate are reached in some cells of histiocytic lines, in monocytes and also in Langerhans dendritic cells. That's why cladribine is highly effective medication in treating Langerhans cell histiocytosis and also in treating diseases of the juvenile xanthogranuloma group. In the paper we present a survey of published experience with cladribine in patients with Langerhans cell histiocytosis. The effectiveness of cladribine in the childhood form of Langerhans cell histiocytosis is investigated only in 1 multicentric clinical study, other data are taken from single case reports or small series studies. Cladribine was used in 60 adult patients altogether and in 51 of them (85%) treatment response (CR + PR) was achieved. In the group of childhood patients cladribine was used in 182 cases and treatment response (CR + PR) was reached in 110 (60.4%) thereof. One possible explanation for a higher number of therapy responses in adults is lower Langerhans cell histiocytosis aggressiveness in adults than in children. Another explanation is the fact that therapy responses in adults are summarized only from case reports and smaller cohorts, whereas in children, case reports and also results of a prospective randomized clinical study are included. Diseases of the juvenile xanthogranuloma group are much more rare than Langerhans cell histiocytosis and so the number of publications is smaller. In total, 7 publications describe therapy response of cladribine in some of the juvenile xanthogranuloma forms (Erdheim-Chester disease, disseminated juvenile xanthogranuloma and localized form of plane xanthoma type). Cladribine was also effective in CNS infiltration by Langerhans cell histiocytosis cells or juvenile xanthogranuloma cells.
Conclusions: Cladribine is a highly effective medication used in treating Langerhans cell histiocytosis. It is very good tolerated in monotherapy. Therefore, it is suitable for initial therapy of adults with multifocal or multisystem form of Langerhans cell histiocytosis. Furthermore, it has the use in treating relapses after some other initial therapy. According to published experience, it is an effective drug for diseases of the juvenile xanthogranuloma group (Erdheim-Chester disease, diffuse juvenile xanthogranuloma and also Rosai-Dorfman disease).