XPO1 and Miyoshi myopathy: The implication of this mechanism in MM drug resistance was first described by Turner et al. in 2004, showing that MM cells actively export endogenous topoisomerase II alpha (TOP2A) toward the cytoplasm during MM cell growth, due to enhanced activity of the Exportin 1 protein (XPO1 or CRM1) (Turner et al., 2004).