JAK1 and macrophage activation syndrome: Ruxolitinib (RUX), a Janus kinase 1/2 (JAK1/2) inhibitor has emerged as a promising therapeutic candidate for MAS, by targeting the JAK1/2-STAT1 signaling pathway, effectively suppressing IFN-γ and other proinflammatory cytokines implicated in MAS pathogenesis (13).