IL1B and sinus histiocytosis with massive lymphadenopathy: The efficacy of cladribine in RDD is felt to be related to its ability to impair monocyte function through interleukin-6 (IL-6), interleukin-1B (IL-1B), and tumor necrosis factor-alpha (TNF-a) inhibition [2,8]. This is supported by a previous report describing the normalization of IL-6 and TNF-a after treatment with cladribine, suggesting the benefit of monitoring pro-inflammatory cytokines to assess response to therapy [8].