Molecular studies have reported that approximately one-third of RDD patients harbor mutations in genes involved in the mitogen-activated protein kinase/extracellular-signal-regulated kinase (MAPK/ERK) signaling pathway, most commonly NRAS, KRAS, and MAP2K1, and more rarely BRAF, supporting a neoplastic rather than reactive etiology [15-17]. Here, MAP2K1 is linked to sinus histiocytosis with massive lymphadenopathy.