Tofacitinib (Xeljanz®) is a potent, selective JAK inhibitor that preferentially inhibits JAK1 and JAK3 used for the treatment of moderate to severe active rheumatoid arthritis (RA) (Table 1) [90-92], Tofacitinib had promising in vitro activity on MM cells [93]. Here, JAK1 is linked to Miyoshi myopathy.