While the cytoreductive properties of cladribine are well established in RDD, further investigation into inhibition of pro-inflammatory cytokines (TNF-a, IL-6, IL-1B) and effect on molecular targets (NRAS, KRAS, MAP2K1, ARAF) may be useful to fully understand the mechanism of response and develop future targeted therapies. This evidence concerns the gene MAP2K1 and sinus histiocytosis with massive lymphadenopathy.